dirstate-v2: Separate HAS_FILE_MTIME and HAS_DIRECTORY_MTIME flags Previously the same flag was used, with its meaning based on whether the node otherwise identifies a file tracked anywhere. In addition to being more explicit, this enables storing a directory mtime if a given path used to be tracked in a parent commit (so the dirstate still has data about it) but became a directory in the working copy. (However this is not done yet as it would require a larger change, replacing the `dirstate_map::NodeData` enum with struct fields.) Differential Revision: https://phab.mercurial-scm.org/D11662