identify: simplify the dirty check This is equivalent to the previous code, but it seems better to be explicit about what aspects of dirty are being ignored. Perhaps they shouldn't be, since the help text says 'followed by a "+" if the working directory has uncommitted changes'. Both merges and branch changes are committable, even if the files are unchanged. Additionally, this will make the `identify` command notice missing subrepo files, once subrepos are taught to look for missing files.

tests: tweak the subrepo dirty state tests This is a continuation of 439b4d005b4a. I overlooked that blackbox logs also have a dirty marker. Also, the `hg update --check` test was updating to a revision where the deleted file wasn't tracked, which is why status seemed to show the deleted file was restored.

match: combine regex code for path: and relpath: The regexes for path: and relpath: patterns are the same (since the paths have already been normalized at the point we create the regexes). I don't think the "if pat == '.'" will have any effect relpath: because relpath: patterns will have the root directory already normalized to '' by pathutil.canonpath() (unlike path:, for which the root gets normalized to '.' by util.normpath()).