Adds search option for best interpolation filter.
Adds a speed feature to conduct a brute force search among a set of available interpolation filters for the best one in an RD sense. There is a gain of 0.4% on derf, 1.0% on Std-HD. Patch 2: A macro added to determine if the encoder state is reset for each new filter tried. Patch 3: rebase, also fixes a bug (decodframe.c) introduced by a couple of missing function pointer assignements. Patch 4: rebase. Change-Id: Ic9ccca9d8c35c6af557449ae867391a2f996cc29