Make the quantizer exact.

This replaces the approximate division-by-multiplication in the
 quantizer with an exact one that costs just one add and one
 shift extra.
The asm versions have not been updated in this patch, and thus
 have been disabled, since the new method requires different
 multipliers which are not compatible with the old method.

Change-Id: I53ac887af0f969d906e464c88b1f4be69c6b1206

vp8/encoder/block.h

@@ -33,6 +33,7 @@ typedef struct
 
     // 16 Y blocks, 4 U blocks, 4 V blocks each with 16 entries
     short(*quant)[4];
+    short(*quant_shift)[4];
     short(*zbin)[4];
     short(*zrun_zbin_boost);
     short(*round)[4];