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.

- correctly trigger done_cb to avoid stuck requests
- pass up an UNAUTHENTICATED status so that clients know what happened

Otherwise we can get a total-queue-ordering violation and complete some
ioreqs out-of-order. This leads to events being pushed to the completion
queue out-of-order, and that leads to applications believing streams are
completed before receiving the last message.