Allow mouse outside of window while paused
This is extremely handy while in windowed mode and done in such programs as WoW.
While the game is running, the cursor stays within the window but when paused the cursor is still tracked in game but is no longer locked/grabbed to the window.
(RM-449 from redmine: created on 2012-11-09 by bret curtis, , closed on 2013-06-16 by Jordan Milne, blocks #523 (closed))