dirstate-v2: Apply SECOND_AMBIGUOUS to directory mtimes too This would only be relevant in contrived scenarios such as a dirstate file being written with a libc that supports sub-second precision in mtimes, then transfered (at the filesystem level, not `hg clone`) to another system where libc *doesn’t* have sub-second precision and truncates the stored mtime of a directory to integer seconds. Differential Revision: https://phab.mercurial-scm.org/D11939