Blender Git Loki

Sequencer: multi-threaded histogram calculation

This gives some percentage of speedup, which compensates slowdown
caused by converting image buffer into display space.

Used OpenMP for this. Still feel skeptic about this, discussed with
Brecht and we decided this approach actually could be used since
seems all the platforms has got OpenMP issues solved.

Waveform and vector scopes are still single-threaded since they're
a bit tricker to be done multi-threaded and probably not so commonly
used.