py3: use setattr() to assign new class attribute The old method produces error 'object does not supports item assignment'. So setattr() is used to assign a new class attribute via __dict__ .

localrepo: use dirstate savebackup instead of handling dirstate file manually This is one step towards having dirstate manage its own storage. It will be useful for the implementation of sql dirstate [1]. This introduced a small test change: now we always write the dirstate before saving backup so in some cases where dirstate file didn't exist yet savebackup can create it. [1] https://www.mercurial-scm.org/wiki/SQLDirstatePlan

localrepo: use dirstate restorebackup instead of copying dirstate manually This is one step towards having dirstate manage its own storage. It will be useful for the implementation of sqldirstate [1]. I'm deleting two of the dirstate.invalidate() calls in localrepo because restorebackup method does that for us. [1] https://www.mercurial-scm.org/wiki/SQLDirstatePlan