Make better use of twisted and its deferred: ProcessProtocol, sockets...

[Antoine Martin]

When starting a process and watching its output, we shouldn't do this in a separate thread but instead integrate the code with twisted main-loop (gtk/glib's actually) using ProcessProtocol?.

When testing for a socket using wait_for_socket, again we should use a twisted protocol to do that.

Finally, when waiting for a process by pid (one we may not have launched ourselves), we should use gobject.child_watch_add(pid) which will also work with the main loop.