Fixes to disable MFQE when there is motion.

This patch includes:
1. fixes to disable block based termporal mixing when motion
is detected (because this version of mfqe only handles zero motion).
2. The criterion used for determining whether to mix or
not are changed to use squared differences rather than
absolute differences.
3. Additional checks on color mismatch and excessive block
flatness added. If the block as decoded has very low activity
it is unlikely to yield benefits for mixing.

Change-Id: I07331e5ab5ba64844c56e84b1a4b7de823eac6cb

vp8/decoder/decodemv.c

@@ -660,4 +660,3 @@ void vp8_decode_mode_mvs(VP8D_COMP *pbi)
         mi++;           /* skip left predictor each row */
     }
 }
-