Early initialisation of thread state.

Ensures that the thread is fully set up (incl. future message queue)
before control is given back to parent.
Initialised the message queue in threads.

Still need to add Grace calls to the post and poll functions in
gracelib_msg.
Actors poll and post functions added.

Inter thread communication using (unsafe) message passing is possible.
Need to figure out how to enfore immutability on the messages (by
copying them? setting a flag?) and make sure they are not GCed when they
are still in scope.