dirstate: move management of nonnormal sets into dirstate map The dirstate map owns the nonnormal sets, and so should be the class to update them. A future implementation of the dirstate will manage these maps differently. The action of clearing ambiguous times is now entirely controlled by the dirstate map, so it moves there too. Differential Revision: https://phab.mercurial-scm.org/D1341

dirstate: add explicit methods for modifying dirstate Instead of assigning dirstatetuple objects to entries in the dirstate, move responsibility for creating tuples into the dirstatemap. Differential Revision: https://phab.mercurial-scm.org/D1340

dirstate: document dirstatemap interface Differential Revision: https://phab.mercurial-scm.org/D1380