convert: add a mode where mercurial_sink skips empty revisions. The getchanges function of some converter_source classes can return some false positives. I.e. they sometimes claim that a file "foo" was changed in some revision, even though its contents are still the same. convert_svn is particularly bad, but I think this can also happen with convert_cvs and, at least in theory, with mercurial_source. For regular conversions this is not really a problem - as long as getfile returns the right contents, we'll get a converted revision with the right contents. But when we use --filemap, this could lead to superfluous revisions being converted. Instead of fixing every converter_source, I decided to change mercurial_sink to work around this problem. When --filemap is used, we're interested only in revisions that touch some specific files. If a revision doesn't change any of these files, then we're not interested in it (at least for revisions with a single parent; merges are special). For mercurial_sink, we abuse this property and rollback a commit if the manifest text hasn't changed. This avoids duplicating the logic from localrepo.filecommit to detect unchanged files.

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