dirstate-item: introduce a `maybe_clean` property It is useful for some extension that seek to invalidate some state. Differential Revision: https://phab.mercurial-scm.org/D11523

dirstate: add a `get_entry` method to the dirstate This method give access to the underlying `DirstateEntry` object (or an empty one if None was there). It should allow us to use the more semantic property of the entry instead of the state where we needs it. Differential Revision: https://phab.mercurial-scm.org/D11522