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

dirstate: add prefix and suffix arguments to backup This would allow the code explicitly copying dirstate to use this method instead. Use of this method will increase encapsulation (the dirstate class will be sole owner of its on-disk storage).

tests: mark test-atomictempfile.py write as binary

tests: mark test-context.py write as binary

transaction: turn lack of locking into a hard failure (API) We have been warning about transactions without locks for about a year (and three releases), third party extensions had a fair grace period to fix their code, we are moving lack of locking to a hard failure in order to protect users against repository corruption.