Explicit MV reference experiment.
Coding and costing of mv reference signal. Issues in updating MV ref with COMPANDED_MVREF_THRESH to be resolved. Ideally the MV precision should be defined based on absolute MV magnitude not as now the MV ref magnitude. Update to mv counts moved into bitstream.c because otherwise if the motion reference is changed at the last minute the encoder and decoder get out of step in terms of the counts used to update entropy probs. Code working on a few test clips but no results yet re benefit vs signaling cost and no tuning of red loop to test lower cost alternatives based on the available reference values. Patch 3. Added check to make sure we don't pick a reference that would give rise to an uncodeable / out of range residual. Patch 6-7: Attempt to rebase. OK to submit but best to leave flag off for now. Patch 9. Remove print no longer needed. Change-Id: I1938c2ffe41afe6d3cf6ccc0cb2c5d404809a712