Blender Git Loki

Sequencer: clear cache and animation buffers for strips outside of cursor when rendering

This avoids having bunch of cached images when doing animation rendering,
keeping all the memory available for rendered itself.

This keeps memory usage low when rendering huge edits with mixed
scenes and movie strips.

This should not affect on sped of video encoding, which was confirmed by
some own tests.

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svn merge -r50051:50052 ^/branches/soc-2011-tomato