util._matcher: speed up regexp matching. In 4babaa52badf, Benoit made a change that substantially slows matching when a big .hgignore file is in play, because it calls into the regexp matching engine potentially hundreds of times per file to be matched. I've partly rolled back his change, so that we only call into the matcher once per file, but preserved the ability to report a meaningful error message if there's a syntax error in the regexp.

Basic install:

 $ make            # see install targets
 $ make install    # do a system-wide install
 $ hg debuginstall # sanity-check setup
 $ hg              # see help

See http://www.selenic.com/mercurial/ for detailed installation
instructions, platform-specific notes, and Mercurial user information.