Dispatching events via |nsIThread| doesn't work with worker threads. This
patch replaces all uses of |nsIThread| in the socket code by equivalent
uses of |MessageLoop|.
The consumer thread handles socket creation, destruction, and
data processing for socket IPC. Traditionally this has been
done on the main thread.
This patch extends the socket IPC classes to support arbitrary
consumer threads. The thread is configured when establishing a
connection, and performs all of the above operations until the
socket is closed.
The new class |ListenSocket| listens on Unix sockets for incoming
connections. Accepted connections are handed over to a compatible
connection-oriented socket.
