bzip2: speed up decompression.
bzip2: speed up decompression.

This borrows a trick from the bzip2 source and effects a decent speed
up when decompressing highly compressed sources. Rather than unshuffle
the BTW block when performing the IBTW, a linked-list is threaded
through the array, in place. This improves cache hit rates.

R=bradfitzgo, bradfitzwork, cw
CC=golang-dev
http://codereview.appspot.com/4247047

wesolows/golang-old,wesolows/golang,wesolows/golang-old,wesolows/golang,firebitsbr/golang-old,wesolows/golang,firebitsbr/golang-old,wesolows/golang,wesolows/golang-old,wesolows/golang-old,wesolows/golang-old,firebitsbr/golang-old,wesolows/golang,wesolows/golang-old,wesolows/golang-old,firebitsbr/golang-old,wesolows/golang,firebitsbr/golang-old,wesolows/golang,firebitsbr/golang-old,firebitsbr/golang-old,firebitsbr/golang-old