Enable the SSE2 4x4 IDCT

This should have been enabled earlier but slipped through.
Using finer quantizer for keyframes

Metrics on video-1-short:
           RATE (%)  DSNR (dB)
    PSNR -0.20639  0.01102
 PSNRHVS -0.16628  0.01316
    SSIM -0.20454  0.00984
FASTSSIM -0.22283  0.01366
Adds optional code to measure the actual overhead of the entropy coder
DC RDO using the actual skip probabilities

video-1-short metrics:
           RATE (%)  DSNR (dB)
    PSNR -0.41900  0.02230
 PSNRHVS -0.47261  0.03719
    SSIM -0.54069  0.02580
FASTSSIM -0.34503  0.02112
Remove unused MV visualization code
detailed accounting
Better MV rate estimation