Disable OBMC + compound

Disable OBMC mode if the current block uses compound prediction.
Results if we only disable this combination for small
block sizes are also listed.

Loss of gain (lowres/midres/AWCYHL)
no compound :         0.230%/0.105%/0.15%
no compound <= 8x8:   0.043%/-0.016%/0%
no compound <= 16x16: 0.153%/0.029%/0.05%


Change-Id: I94c9d704172dd02e53f3b2004a8032a4f1265057