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.