Clean ups and minor changes in high precision mv with 8-tap interpolation

* Removes EDGE_PIXEL_FILTER for external sanpshot
* changes the default 8-tap filter based on high precision results
in http://www.corp.google.com/~debargha/vp8_results/enhinterpn.html
* changes the default prob tables for high-precision mv encoding to
favor zeros in the last bit (i.e. quarter pel). This is only important
for short clips.

Change-Id: I02bb0de8679d9eec06cdbcc8160dbf073cd847a4
3 files changed