fix decoding of qtrle codec and possibly others

fix decoding of qtrle codec and possibly others
we rely on ffmpeg calling context->get_buffer, which we override to
point to our get_frame_buf(),  to stuff our pts values into frames it
is decoding. but some decoders call context->reget_buffer
instead.  So I added an override for this callback as well.

git-svn-id: svn://localhost/HandBrake/trunk@3262 b64f7644-9d1e-0410-96f1-a4d463321fa5