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.
# should show copy
copy: foo -> bar
# shouldn't show copy
# should match
rev offset length base linkrev nodeid p1 p2
0 0 5 0 0 2ed2a3912a0b 000000000000 000000000000
bar renamed from foo:2ed2a3912a0b24502043eae84ee4b279c18b90dd
# should not be renamed
bar not renamed
# should show copy
copy: foo -> bar
# should show no parents for tip
rev offset length base linkrev nodeid p1 p2
0 0 69 0 1 6ca237634e1f 000000000000 000000000000
1 69 6 1 2 7a1ff8e75f5b 6ca237634e1f 000000000000
2 75 82 1 3 243dfe60f3d9 000000000000 000000000000
# should match
rev offset length base linkrev nodeid p1 p2
0 0 5 0 0 2ed2a3912a0b 000000000000 000000000000
1 5 7 1 2 dd12c926cf16 2ed2a3912a0b 000000000000
bar renamed from foo:dd12c926cf165e3eb4cf87b084955cb617221c17
# should show no copies