New inter mode context.
This patch creates a new inter mode contest that avoids a dependence on the reconstructed motion vectors from neighboring blocks. This was a change requested by a hardware vendor to improve decode performance. As part of this change I have also made some modifications to stats output code (under a flag) to allow accumulation of inter mode context flags over multiple clips Some further changes will be required to accommodate the deprecation of the split mv mode over the next few days. Performance as stands is around -0.25% on derf and std-hd but up on the YT and YT-HD sets. With further tuning or some adjustment to the context criteria it should be possible to make this change broadly neutral. Change-Id: Ia15cb4470969b9e87332a59c546ae0bd40676f6c