This commit hooks up the rate-distortion optimization system to
fully exploit recursive transform block partition and multiple
transform type. The compression performance of the two experiments
largely adds up. For derf set, ext-tx provides additional 2.1%
coding gains on top of the gains due to recursive transform block
partition (0.69%).

Change-Id: I1091fb9545f74e489a6a2489dc3c12f5abd05043