This patch removes the need for a separate warp_affine_post_round
function by adding the functionality to the warp_affine function.

The encoded output should remain unchanged, but the encoder/decoder
should operate faster because the sse2 and ssse3 warp implementation
can now be used when post_rounding is being used.

Change-Id: Ide52cae55de59a9da9c27c5793e17390f6d2c03e