dirstate: replace the use of _normallookup in `setparents` normal lookup is a complicated function that we want to get rid of. Differential Revision: https://phab.mercurial-scm.org/D11431

dirstate: introduce a set_tracked method on "map" and "item" This move more implementation details withing the DirstateItem itself, which is what we have been doing for a while. Differential Revision: https://phab.mercurial-scm.org/D11430

dirstate: fix restoration of "merged" state after a remove Before this change, "merged" file that get removed and re-added later were recorded as "from_p2" instead. This came from 8fe74328f700, a 2014 changeset that start explicitly doing so for reason I have not been able to fully grasp. The graft test mentioned in the description are still happy after this changeset. So this changeset restore what seems to be the intended behavior. Restoring information as it was before the removal. Differential Revision: https://phab.mercurial-scm.org/D11429

dirstate: inline the last two `_drop` usage The function is small and having the associated code directly inline help use to cleanup the dirstate API. Differential Revision: https://phab.mercurial-scm.org/D11428

dirstate: make a conditionnal easier to read in `setparents` By grabing `nullid` in the local space, we get the conditionnal to fit in one line. Differential Revision: https://phab.mercurial-scm.org/D11427

dirstate: removed the now unused `_add` method Differential Revision: https://phab.mercurial-scm.org/D11426