Add a way to concatenate lists without losing data when one or more of the lists was written using a newer version of the protocol.

Fix bug causing exception: "'Disembargo' of type 'senderLoopback' sent to an object that does not point back to the sender."

The problem happened when pipelined calls were made on a promised capability, but then that capability turned out to be null. The promise resolving code incorrectly interpreted this as the remote promise having resolved to a local capability (because the "null" stub capability looks local), and so it would send a Disembargo message to flush the pipeline as required. However, the remote end would receive this Disembargo message and find it is addressed to a null capability, not a capability pointing back to the sender. This was treated as a protocol error, causing the receiver to close the connection.

The solution is to explicitly identity "null" capabilities so that we can distinguish this case. This change also has the benefit that now when you copy a null capability between messages with foo.setCap(bar.getCap()), the pointer will be set null in the destination, rather than becoming a reference to a local broken capability.

Thanks to David Renshaw for narrowing this down.

Also introduce a way to copy a struct or list which applies membranes to all embedded capabilities, since this seems like it will be needed in conjuction with the above.

**The problem**

The methods MessageReader::initCapTable() and MessageBuilder::getCapTable() always felt rather hacky. initCapTable() in particular feels like something that should be handled by the constructor. However, in practice, the cap table is often initialized based on a table encoded within the message itself. That is, an RPC message contains a "payload" which includes both the application-level message structure and a table of capabilities. The cap table has to be processed first, then initCapTable() is called on the overall message, before the application structure can safely be read.

The really weird part about this is that even though the cap table only applies to one branch of the message (the payload), it is set on the *whole* MessageReader. This implies, for example, that it would be impossible to have a message that contains multiple payloads. We haven't had any need for such a thing, but an implemnetation that has such artificial limitations feels very wrong.

MessageBuilder has similar issues going in the opposite direction.

All of this ugliness potentially gets worse when we introduce "membranes". We want a way to intercept capabilities as they are being read from or written to an RPC payload. Currently, the only plausible way to do that is, again, to apply a transformation to all capabilities in the message. In practice it seems like this would work out OK, but it again feels wrong -- we really want to take a single Reader or Builder and "wrap" it so that transformations are applied on capabilities read/written through it.

**The solution**

This change fixes the problem by adding a new pointer to each struct/list Reader/Builder that tracks the current cap table. So, now a Reader or Builder for a particular sub-object can be "imbued" with a cap table without affecting any other existing Readers/Builders pointing into the same message. The cap table is inherited by child Readers/Builders obtained through the original one.

This approach matches up nicely with membranes, which should make their implementation nice and clean.

This change unfortunately means that Readers and Builders are now bigger, possibly with some performance impact.

Fix bug where calling a list setter using a list obtained from a similarly-typed getter, but where the underlying pointer was null, would write an incorrectly-typed pointer in the destination (specifically, an empty List(Void)). Now it sets an empty list of the correct type.

Fix bug where capability pointers were corrupted when 'transferred', e.g. using adoptWithCaveats() or truncate().

Unfortunately, commit 10487060 missed a case of CPU amplification via struct lists with zero-sized elements.

See advisory: https://github.com/sandstorm-io/capnproto/blob/master/security-advisories/2015-03-05-0-c++-addl-cpu-amplification.md

Deep-clear target object when overwriting pointer. (Minor bug I noticed while working on other things.)

Details: https://github.com/sandstorm-io/capnproto/tree/master/security-advisories/2014-03-02-0-all-cpu-amplification.md

Details: https://github.com/sandstorm-io/capnproto/tree/master/security-advisories/2014-03-02-1-c++-integer-underflow.md

Details: https://github.com/sandstorm-io/capnproto/tree/master/security-advisories/2014-03-02-0-c++-integer-overflow.md

The project file still only compiles a test binary, but it should be easy to separate out a library project from here.

Thanks again to Bryan Boreham <bjboreham@gmail.com> for much help getting this working.

The 'objectId' field is now deprecated. Long-term, each vat will export no more than one "bootstrap interface" which can be obtained via 'Bootstrap'. Restoring SturdyRefs will be accomplished through higher-level interfaces specific to the VatNetwork in use.

See comments for 'Bootstrap' in rpc.capnp for more discussion.

Extended discussion:
https://groups.google.com/d/msg/capnproto/lRlWBOglQv4/8-Qo96AcZQIJ

Extended discussion:
https://groups.google.com/d/msg/capnproto/lRlWBOglQv4/8-Qo96AcZQIJ

To use, pass --disable-reflection to the configure script.

This produces a smaller runtime library. However, using it for this purpose is not recommended. The main purpose of lite mode is to define a subset of Cap'n Proto which might plausibly compile under MSVC. MSVC still lacks full support for constexpr and expression SFINAE; luckily, most of our use of these things relates to reflection, and not all users need reflection.

Cap'n Proto lite mode inherits its name from Protocol Buffers' lite mode. However, there are some key differences:

- Protobuf generated code included global constructors related to registering descriptors and extensions. For many people, this was the main reason to use lite mode: to get rid of these global constructors and achieve faster startup times. Cap'n Proto, on the other hand, never had global constructors in the first place.

- Schemas are actually still available in lite mode, though only in their raw (Cap'n Proto structure) form. Only the schema API (which wraps the raw schemas in a more convenient interface) and reflection API (which offers a convenient way to use the schemas) are unavailable.

- Lite mode is enabled in an application by defining CAPNP_LITE rather than by specifying an annotation in the schema file. This better-reflects real-world usage patterns, where you typically want to enable lite mode application-wide anyway.

- We do not build the lite mode library by default. You must request it by passing --disable-reflection to the configure script. Before you can do that, you must have a prebuilt Cap'n Proto compiler binary available, since the compiler can't be built without reflection.

- Relatedly, the lite mode library is built with the same name as the full library. This library is not intended to be installed. If anything it should be statically linked. But, mostly the option only exists on non-MSVC platform to give us a way to test that we haven't broken lite mode.

For portions currently copyright by Kenton (most of it), transfer copyright to Sandstorm Development Group, Inc. (Kenton's company).

The license change is practically meaningless, as MIT and BSD 2-clause are legally equivalent. However, the BSD 2-clause license is sometimes confused for its ugly siblings, BSD 3-clause and BSD 4-clause. The MIT license is more immediately recognizeable for what it is.

Rémy Blank and Jason Choy (the two non-trivial contributors) are on record as approving this change:

https://groups.google.com/d/msg/capnproto/xXDd2HUOCcc/gbe_COIuXKYJ

Add ability to truncate a list post-allocation and reclaim space. Currently limited to blobs and can only be accessed through the Orphan interface.

Make it possible for a message builder to incorporate a byte array not owned by it without copying.  Useful for injecting large data blobs into a message without copying their contents.  Access this functionality through the Orphanage interface.

Fixes #67.  Also, prevent people from accidentally making MessageBuilder subclasses copyable/movable as brought up in issue #64.

Eliminate the concept of imbuing messages in favor of the simpler concept of setting a cap table directly on MessageReader / getting one from MessageBuilder.  This eliminates capability-context entirely.  This was made possible by the earlier change which moved capabilities to a separate table rather than storing CapDescriptors inline, but I didn't realize it at the time.

Hack to make it safe to read capabilities from default values (returning broken caps) without introducing a dependency from libcapnp on libcapnp-rpc.

Extend totalSizeInWords() to also return a count of capabilities, which helps when a separate capability table needs to be allocated as well.  Use this in the RPC system.