tests: relax "Connection refused" match We already had the match relaxed on Windows, but on Google Compute Engine VMs I'm seeing "Network is unreachable" instead of "Connection refused". At this point, just give up and make sure we get an error back.

commandserver: backport handling of forking server from chgserver This is common between chg and vanilla forking server, so move it to commandserver and unify handle(). It would be debatable whether we really need gc.collect() or not, but that is beyond the scope of this series. Maybe we can remove gc.collect() once all resource deallocations are switched to context manager.

commandserver: promote .cleanup() hook from chgserver This allows us to unify _requesthandler.handle().

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.

sslutil: move context options flags to _hostsettings Again, moving configuration determination to a single location.

sslutil: move protocol determination to _hostsettings Most of the logic for configuring TLS is now in this function. Let's move protocol determination code there as well.