[Twisted-Python] callFromThread with return

[Glyph Lefkowitz]

Andrew, can you add a bug to the tracker for this, and assign it to 
someone? :)  It would also be good if it did handle Deferreds, but I'm a 
little sketchy on where the callback would go (I mean, you're in a 
thread because you're blocking already, right?  but deferreds are to 
avoid blocking, so does that mean the callback runs in a thread or in 
the main loop?)