Fixes #90. The bug causes floating-point fields with non-zero defaults to be corrupted if they are set to NaN on a MIPS machine.

Only available when KJ_STD_COMPAT is defined.

This allows {schema,rpc,rpc-twoparty}.capnp to be used without modification when
relocated outside of the Cap'n Proto codebase.

Add loadCompiledTypeAndDependencies() to SchemaParser so that compiled constants can be cast to static types.

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

I decided that consistent output across platforms is an important property, worth sacrificing a little bit of performance on MIPS.

Otherwise, at least clang++, forward-declares it inside the namespace `::capnp` and doesn't match it with a real `struct sockaddr` from the header 'socket.h'.

Also, accept `const` pointer - there is no point not to do so.

- Define separate times for durations vs. absolute times.
- Make more consistent with existing precedents in KJ style.

Apparently writev() imposes a limit on the vector size.  Work around that.  Not sure why libc doesn't already do this.