Blender Git Loki

Made it so avi code handles "dropped frames"

some avi's have 0 sized chunks that we were not handling properly.
(Need to basically rewind the avi to previous frame in this case)

http://www.cs.umn.edu/~mein/blender/avi/examp.avi has 25 frames,
4,7 and 9 are "dropped frames"

blender use to crash on these now it displays the frame before it assuming
there is one.

Kent