- Modified temporal filter to take extra buffer parameter
- Added bilinear interpolation, can be turned on by setting
BGSPRITE_INTERPOLATION define to 1.
- Added mean filter to bgsprite for blending modes
- Bilinear interpolation is turned OFF by default
- Mean filtering turned ON by default (was previously median filtering)
- Allow for multiple references for alt_ref in encodeframe

Change-Id: Icfe9054049339d353b4befff11e96c12ca73ed4e