This adds movieclip input support to the sequencer, thereby making
undistorted and stabilized footage available without a seperate render step.
Also: removes some old cruft code from the sequencer:
* new_tstripdata wasn't used anymore
* StripElems were allocated for SCENE strips on full length, wasting memory
Added a comment, that hopefully makes things a little bit clearer:
StripElems are *only* usefull for MOVIE + IMAGE strips for all other strip
types one can set this pointer to NULL. (If that should cause otherwise
problems, then the code that doesn't check for NULL is to blame!)
