ADD: Experimental Movie player stim (MovieStim2)

See Movie2Stim.py in demos for an example and for details on status of
implementation.

Please let me know how it works for you; has not been tested on OS X,
only Windows and Linux.
Merge branch 'master' of git://github.com/psychopy/psychopy
ENH: MovieStim2 seek() supported.

Can now seek forward / backward in movie.
ENH: Rearranged MovieStim2 comments

- Moved stim status and notes to stim class module and removed from
demo.
- Removed some prints
- Changed a couple method doc strings to remove reference to avbin
Merge pull request #567 from isolver/master

ADD Experimental MovieStim2 class; avbin free.