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
Set StepsTypeStr in Steps::CreateBlank.
Merge branch 'UnknownStyleSupport' of https://github.com/kyzentun/stepmania
Fixed UnknownStyleSupport.
Don't crash if AI.ini doesn't exist.
Added StageStats:GetStepsSeconds lua function.
Added lerp, lerp_color, approach, and multiapproach lua functions.
Merge pull request #349 from kyzentun/LerpColor

Lerp and related math functions.
Fix P2 input when PlayerAutoplay in P1
Merge pull request #352 from hanubeki/input-p2

Fix P2 input when PlayerAutoplay in P1
Lineage reporting for nil commands in RunCommands.  Stricter type checking for FormatPercentScore in PercentageDisplay.
Changed ColorToHex to just use string.format instead of useless number to hexstring to number to hexstring conversion.
Fixed broken else-if chain in Actor::SetEffectClockString.  Changed error to not crash Stepmania.
Minor docs change for effect colors.
Fixed coloring and cropping of RollingNumbers during tweens.
Fixed RollingNumbers to work with corner diffuse colors.  Changed diffuse loops to use NUM_DIFFUSE_COLORS instead of 4.
Created tween queue and functions for BitmapText so the stroke color can be tweened.
Merge pull request #362 from kyzentun/StrokeTween

Tweenable stroke color for BitmapText