Patch from Joakim Tjernlund <joakim.tjernlund@lumentis.se>

I did the optimizations in the crc32 patch Brian Murphy submitted a while ago.
Now I have cleaned it up a little and made some more optimizations.

gcc is quite bad at loop optimizations (at least for PPC) so I have
rewritten them to make gcc to generate better code. Even recent gcc's(3.2.x) produces
better code.

Also reduced the unrolling since it did not make a noticeable difference.