Segmentation experiment:

Added last_segmentation_map[] structure
to keep track of what we had before when
doing temporal prediction. With this change
the existing code does once again appear to
be giving a decodable bitstream for both
temporal and standard prediction modes.
However, it is still somewhat messy and
confused and there is no option to take
advantage of spatial prediction so it could
do with further work.

Some housekeeping / clean out.

Change-Id: I368258243f82127b81d8dffa7ada615208513b47