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.
#!/bin/sh
hg init a
cd a
echo bar > foo
hg add foo
hg ci -m 'add foo' -d '1000000 0'
echo foobar > foo
hg ci -m 'change foo' -d '1000001 0'
echo 'quiet:'
hg --quiet diff -r 0 -r 1
echo
echo 'normal:'
hg diff -r 0 -r 1
echo
echo 'verbose:'
hg --verbose diff -r 0 -r 1
echo
echo 'debug:'
hg --debug diff -r 0 -r 1
echo