Blender Git Loki

General cleanup in sequencer:

- Seperated StripData into
StripData
TStripData
where StripData holds only image-filenames and TStripData holds
the working information needed for ImBuf caching.
=> Large drop in memory usage, if you used a lot of movie and meta strips.
=> Fixed bugs in "duplicate" on the way (imbufs where copied around without
taking reference counting seriously...)
=> Code is much cleaner now
- Added defines for TStripData->ok
Finally figured out, what the magic values ment and named them properly :)
- Got rid of Sequence->curelem.
Reason: very bad idea(tm) for multi threading with more than one render
thread. Still not there, but this was a real show stopper on the way.