This completes issue #726. All that cascading activation stuff just
didn't work out as cleanly as I had hoped it would.

- avoid string copy due to google::protobuf::message::SerializeToString
- avoid string copy due to google::protobuf::message::ParseFromString
- split large message into 8k slices during protobuf serialization
- correct GrpcBufferReader::BackUp

Signed-off-by: Ronnie Sahlberg <ronniesahlberg@gmail.com>

Change all !str[n]cmp to be str[n]cmp == 0 consistently across the codebase.

Issue #231

Signed-off-by: Ronnie Sahlberg <ronniesahlberg@gmail.com>

The assembly and face layers were mostly redundant except that the
assembly layer had far-better interfaces and the face layer had more
of a reason to exist. Now they are merged.

Also refactor the interop package to perform client-server interop
testing in a unit test.

This optional value should only be passed in tests.

Add synchronization in server_secure_chttp2.c to avoid propagating a
completed handshake past that layer to a potentially already destroyed
server.