daemon: allow synhesizing-only clients to register without commands.
w3c-speech: initial W3C speech API plugin and test client implementation.

The primary purpose of the W3C speech plugin is to server as
the backend for implementing the W3C Speech API for Crosswalk.

See README.protocol for a description of the protocol implemented
by the plugin.
w3c-speech: don't compile w3c-message.c.
native-client: change to use unix domain socket by default.