Revert "Preserve Steps of unknown Style."

This reverts commit 8edd929e24025d8b39aa337e950fe1ce227b459a.

This also updates the song cache.
Merge pull request #341 from wolfman2000/wolf-revert-style-preserve

Revert "Preserve Steps of unknown Style."
modify StretchNoLoop and StretchRewind to only run certain commands if they exist.
fixes issue #337

I also modified StretchNoLoop to start at the beginning of the movie to prevent it from freezing on the last frame (which I'm assuming is not the intended behavior; let me know if that's wrong)
update changelog with the last fix; SM5 beta 4a shortly.
changelog cleanup on aisle 5; this feature was just reverted, oops sorry