added main_loop.TornadoEventLoop implementation

tested with Python 2.7 and 3.3
added TornadoEventLoop import to __init__.py
more robust poll object patching (works on Linux, *BSD & OSX)
replaced WeakValueDictionary with a simple dict in TornadoEventLoop
revert whitespace changes
always import GLibEventLoop and TornadoEventLoop
see: from __future__ import braces
Merge TornadoEventLoop from aglyzov

Conflicts:
	urwid/main_loop.py
TornadoEventLoop: use new shared event loop tests
test for exception due to user encoding
fix for exception due to user encoding
fix TornadoEventLoop enter idle
fix TornadoEventLoop remove_alarm
travis: add tornado dep
fix Terminal: retry on select interrupted
Merge branch 'tornado'