[Urwid] Twisted version of generic_main_loop

[Ian Ward]

Walter Mundt wrote:
> I just hacked this up last night so no guarantees that it's
> perfect...but here's a twisted_main_loop that's very similar in nature
> and functionality to the generic_main_loop in the current urwid checkout
> -- except that everything run from inside of it happens in the context
> of a Twisted reactor.
> 
> It places a blocking input loop in a separate thread, but arranges for
> the actual input processing to happen inside the main reactor thread so
> that this shouldn't cause any real issues.

Thanks Walter,

It's a good start.  I was hoping this could be done with
get_input_descriptors[1] and get_input_nonblocking[2] instead of using
threads.

[1] http://excess.org/urwid/reference.html#Screen-get_input_descriptors
[2] http://excess.org/urwid/reference.html#Screen-get_input_nonblocking

Ian