ui: provide official way to reset internal state per command This will allow us to clear in-memory password storage per runcommand(). I've updated commandserver to call resetstate() of both ui and repo.ui because they may have different states in theory.

revset: extract function that validates sort() arguments This function will be used in _optimize() to get rid of noop sort() call while validating its arguments.

revset: build dict of extra sort options before evaluating set Prepares for extracting a function that only validates sort options.

revset: build list of (key, reverse) pairs before sorting Prepares for extracting a function that only validates sort options.

revset: fix crash on empty sort key Make it noop as before 2188f170f5b6. We could change it to an error, but allowing empty key makes some sense for scripting that builds a key string programmatically.

rebase: move local variable 'targetancestors' to the RR class