largefiles: don't assume that .hg/largefiles/ still exists It might not have been created and it might have been removed.

largefiles: getstandinmatcher should not depend on existence of directories Looking for a (potentially empty) directory was not reliable - both because it is a reasonable assumption that empty directories can be removed and because it wasn't created in all cases ... such as when pulling to an existing repository.

tests: don't rely on broken behaviour in test-largefiles-cache.t The test relied on the bug that 'pull largefiles from branchheads' didn't pull any largefiles from tip revision when it seemed like no largefiles had been checked out before.