Super-elegant patch by Tim Peters that speeds up colorization

Super-elegant patch by Tim Peters that speeds up colorization
dramatically (up to 15 times he claims).  Works by reading more than
one line at a time, up to 100-line chunks (starting with one line and
then doubling up to the limit).  On a typical machine (e.g. Tim's
P5-166) this doesn't reduce interactive responsiveness in a noticeable
way.