Adjusting 8-tap filter + prelim edge pixel filter code.

Adjusting 8-tap filter + prelim edge pixel filter code.

Results with the new filter coefficients compared with the previous
versions are here:
http://www.corp.google.com/~debargha/vp8_results/enhinterp.html (derf)
http://www.corp.google.com/~debargha/vp8_results/enhinterp_hd.html (HD)
Overall, the derf set improves by 0.94% with 8-tap filters while
the HD set improves by 0.58%.

Patch 1: resolving merge conflict

Change-Id: I09db0abdab7b08bb19f86d911de23d2123309748