- Add unit tests to verify the bit-exact result.
- User level time reduction (EXT_TX):
    encoder: 3.63%
    decoder: 2.36%
- Also add tx_type=V_DCT...H_FLIPADST SSE2 for 16x16 inv txfm.

Change-Id: Idc6d9e8254aa536e5f18a87fa0d37c6bd551c083