quant: remove extra upshift by 4 in s_invQuantScales

Adding 4 to unQuantPer was a bug, since unQuantScale was already upshifted by 4.
quant: simplify UNQUANT() variables
quant: update comment for UNQUANT macro
quant: typo
fix HIGH_BIT_DEPTH compile on Windows

something included by predict.h breaks pixel-util.h for MSVC; so move the filter
table to common.h. It wasn't quite proper for asm-primitives.cpp to include a
header from encoder/ anyway.