Mark every destructor "noexcept(false)" unless it is very clearly noexcept.  The change in C++11 making destructors default-noexcept was a mistake.

Replace most CAPNPROTO_ASSERTs with the new logging/error macros.  Also add a SYSCALL macro and use it.  Also add commentary.

Improve eval benchmark message structure to waste fewer objects (for both protobuf and capnproto, but this turns out to help capnproto more than protobufs).