rhg: implement checkexec to support weird filesystems In particular, some of our repos are stored on a fileserver that simulates POSIX permissions poorly, in such a way that prevents the removal of execute permission. This causes rhg show a spurious unclean status, even though python hg reports the repo as clean. We fix this by making rhg implement the ~same checkexec logic that python hg does.

typing: use python3-style type annotation

merge: cache the fs checks made during [_checkunknownfiles] this ~halves the number of lstat calls made when updating from rev(-1) to a revision with lots of files

merge: disable the whole filesystem access loop if [_realfs] is false This makes it clearer that [auditeddir] is only relevant for [_realfs] checkers, and makes the non-realfs checkers more performant.

merge: short-circuit the _checkfs loop upon getting ENOENT This reduces the number of [lstat] calls when updating from rev(-1) to a rev with lots of files by a factor of several: for path foo/bar/baz/quux.txt without this patch we're lstatting: foo foo/bar foo/bar/baz foo/bar/baz/quux.txt and with this patch: foo foo/bar/baz/quux.txt

merge: don't pay for pathconflicts if there are none

pathauditor: no need to normcase the paths The only thing normed paths are used is the key of the caching sets, so the only change of behavior will be that the checks will be repeated for paths that differ by case. If anything, it seems correct for the check to be repeated, in case that actually affects semantics, but the main reasoning is simplifying the code and making it a bit faster. It looks like the code originally comes from commit [081e795c60e0]: it looks like that commit tried to get rid of the existing norming, but presumably did this overly cautiously, preserving it for the cache keys, even though it was pointless even then.