optimize copyMacroblock by keeping partial sums and reusing them. Also cleanup.
optimize copyMacroblock by keeping partial sums and reusing them. Also cleanup.

Signed-off-by: Dominic Szablewski <1d6e1cf70ec6f9ab28d3ea4b27a49a77654d370e@phoboslab.org>

phoboslab/jsmpeg,PetroCloud/jsmpeglive,faljse/jsmpeg,PetroCloud/jsmpeglive,phoboslab/jsmpeg,seiche/VidSocket,faljse/jsmpeg,phoboslab/jsmpeg,PetroCloud/jsmpeglive,faljse/jsmpeg,phoboslab/jsmpeg