Merged the enhanced_interp experiment.
Found and fixed a bug in the include files framework, whereby
certain encoder files were still using the old INTERP_EXTEND
value of 3 instead of 4. The thresholds for mv range mcomp.c
need a small adjustment to prevent crashes.

The results are more or less unchanged.

Change-Id: Iac5008390f1efc97ce1102fbb5f8989c847fb579