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.
% new file
applying patch from stdin
% new empty file
applying patch from stdin
empty
% chmod +x
applying patch from stdin
% copy
applying patch from stdin
a
a
% rename
applying patch from stdin
copyx
empty
new
rename
% delete
applying patch from stdin
empty
new
rename
% regular diff
applying patch from stdin
% copy and modify
applying patch from stdin
a
a
b
a
a
% rename and modify
applying patch from stdin
a
a
b
c
a
% one file renamed multiple times
applying patch from stdin
9 rename2 rename3 rename3-2 / rename3 (rename2)rename3-2 (rename2)
rename3
rename3-2
a
a
b
c
a
a
a
b
c
a
% binary files and regular patch hunks
applying patch from stdin
foo
045c85ba38952325e126c70962cc0f9d9077bc67 644 binary
% many binary files
applying patch from stdin
045c85ba38952325e126c70962cc0f9d9077bc67 644 mbinary1
a874b471193996e7cb034bb301cac7bdaf3e3f46 644 mbinary2