Blender Git Loki

Ultra hacky fix for sequencer:

Avoid opening the file when doing uncached reading because ffmpeg takes
quite a long time to read the first frame. Instead, avi jpeg is almost
instantaneous here.
This will leave the anim struct without an Imbuf and that can cause
other unexpected issues elsewhere so commiting on gooseberry first
to try.
Speedup is quite impressive though.

Needless to say, code here quickly becomes a mess and the proxy system
should be made saner but for now just commit to keep things working at
the studio.