commandserver: extract method to create commandserver instance per request This is a step toward merging chgserver._requesthandler with commandserver's.

error: make hintable exceptions reject unknown keyword arguments (API) Previously they would accept any typos of the hint keyword.

error: make HintException a mix-in class not derived from BaseException (API) HintException is unrelated to the hierarchy of errors. It is an implementation detail whether a class inherits from HintException or not, a sort of "private inheritance" in C++. New Hint isn't an exception class, which prevents catching error by its type: try: dosomething() except error.Hint: pass Unfortunately, this passes on PyPy 5.3.1, but not on Python 2, and raises more detailed TypeError on Python 3.