BF: Updated rush() on all platforms

- added realtime kwarg to function signature.
- realtime kwarg currently only used on Windows
- allows same script that calls "rush(realtime=True)" to be used
regardless of OS.
Merge branch 'master' of git://github.com/psychopy/psychopy
Merge pull request #710 from isolver/master

Added 'realtime' kwarg to rush() function on all platforms