Improves function to return sad of integer pels by reusing integer
pels already visited in the smallest scale.
Turns on BIGDIA search for speed 4. Also, turns on the
first version of the pruned subpel search at this speed.

derf: -0.32% (speed 4)

Speed seems to improve by at least 5% but subject to verification.

Change-Id: Iaec8eaffd61d6237ac029e6a2a1b0a88b2a35271