Adds a new command to super-test.sh:

  ./super-test.sh cmake-package <config>

where <config> is one of:

- autotools-shared
- autotools-static
- cmake-shared
- cmake-static

This command tests the CMake config package files installed by the given build configuration. For now, that test consists of building the samples against an installation of Cap'n Proto.

These variables need to be cache variables or else the user can't override them on the command line (e.g. when building a project against a lite mode installation).

No change in behavior, but the comments needed updating, so I updated them.
Then I noticed a never-true if() case and removed it.

Closes #523.

Copied CMake's bundled AnyNewerVersion template to our local cmake/ directory, and modified both CMake and autotools scripts to configure/install it.

This completes the autotools installation of CMake config files, minus version compatibility checking.

Includes a small refactor to eliminate the need to maintain two copies of
the list of .pc files. (Note: there's actually a third copy of the list in
CMakeLists.txt.)

Includes a small refactor to make adding filenames simpler.

kj-test and kj-http currently have their headers installed, and the CMake
build exports them as targets, so I'm adding .pc.in files for them. I
initially added capnpc as well, but that appears to be a private API.

Memcpy null src

Revert "Don't read past the end of the base64 decode out buffer."

Don't read past the end of the base64 decode out buffer.

Don't bind Header reference to a null pointer.

Variable-length arrays must have positive bound.

It is invalid to pass null as a pointer argument to memcpy/memcmp/memset, even if the count argument is zero:

> Where an argument declared as size_t n specifies the length of the array for a
function, n can have the value zero on a call to that function. Unless explicitly stated
otherwise in the description of a particular function in this subclause, pointer arguments
on such a call shall still have valid values [...]

Detected by -fsanitize=nonnull-attribute.

If we finish decoding in step_a state, there is no current output character, so reading *plainchar will either be an uninitialized read or (if the output buffer is minimally sized) a past-the-end read.

Detected by -fsanitize=address.

If recvData is empty, recvData.begin() is a null pointer and binding a Header reference to it is invalid.

Detected by -fsanitize=null.

Detected by -fsanitize=vla-bound

Generate ASLR-friendly numeric stack traces.

Add Own<T>::attach() which is much like Promise<T>::attach()

We don't support any extensions currently, but it's important that when acting as a proxy, we don't pass through this header, since it could result in the client and server negotiating extensions that the proxy doesn't understand and will botch.

This is definitely wrong, because it makes the read/write tasks impossible to cancel and possibly makes them outlive the buffers they are reading from / writing to.

I have no idea why I wrote the code this way, TBQH.