[Telepathy] new Gabble test infrastructure

[Dafydd Harries]

I've just merged to Gabble some test infrastructure based on the Twisted async
Python framework. There are few tests that use this framework, but we'd like to expand our test coverage.

Senko and I managed to use VNC in conjunction with a Telepathy voice call to
write a regression test for a bug he was fixing. I think it's easier for me to
show somebody the process of writing these tests than to try and explain it,
so I'm happy to do similar things with other people.

How it works:

The infrastructure code. emulates a Jabber server. Eeach test is a series of
functions which are called when events happen. An event is either a D-Bus
signal, or an XML stanza. Each function is called repeatedly until it removes
itself from the queue.

-- 
Dafydd