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.
adding a
adding b
adding dir.h/foo
adding t.h
adding t/b
adding t/e.h
adding t/x
hg locate a
a
locate succeeded
hg locate NONEXISTENT
locate failed
hg locate
a
b
dir.h/foo
t.h
t/b
t/e.h
t/x
hg locate a
hg locate NONEXISTENT
hg locate relpath:NONEXISTENT
hg locate
b
dir.h/foo
t.h
t/b
t/e.h
t/x
hg locate -r 0 a
a
hg locate -r 0 NONEXISTENT
hg locate -r 0 relpath:NONEXISTENT
hg locate -r 0
a
b
dir.h/foo
t.h
t/b
t/e.h
t/x
% -I/-X with relative path should work
hg locate
b
dir.h/foo
t.h
t/b
t/e.h
t/x
hg locate -I ../t
t/b
t/e.h
t/x
hg locate t/**
t/b
t/e.h
t/x
hg locate b
../b
../t/b
hg locate *.h
../t.h
../t/e.h
hg locate path:t/x
../t/x
hg locate re:.*\.h$
../t.h
../t/e.h
hg locate -r 0 b
../b
../t/b
hg locate -r 0 *.h
../t.h
../t/e.h
hg locate -r 0 path:t/x
../t/x
hg locate -r 0 re:.*\.h$
../t.h
../t/e.h