Fix but where interface server's transitive superclass's methods weren't dispatched correctly -- ouch.

Not everyone has `nproc`. In particular it does not appear to be present on my OSX build. Better to leave a fixed number here. This is just a suggestion anyhow.

This reverts commit 9c18f2ad.

Add asGeneric() methods to generic readers, builders, and interfaces which casts them to the same type but with different generic parameters.

Provide a way to get the ClientHook out of a Capability::Client, needed by third-party RPC/storage/etc systems.

Add CVE numbers to security advisories. Source: http://www.openwall.com/lists/oss-security/2015/03/17/3

Hardcode /bin/cat output option for `capnp compile`.

Implement CapabilityServerSet which provides a way to unwrap loopback capabilities to get the underlying server object, and also implements weak references.

Update comparison blog post to note that proto3 removes unknown field retention, for some ridiculous reason.

zero warnings: use KJ_UNUSED for unused constexpr & local vars

Ignore stuff that needs ignoring.

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

one function in arena.c++ and several snprintf_result local vars
in string.c++ get optimized away because they're only used in
KJ_DASSERT() invocations.

this patch thus identifies those unused declarations with KJ_UNUSED

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