Attached is a second patch that adds keyword-only argument support to PyArg_ParseTupleAndKeywords.  This was developed in isolation.

The magic character is '$'; I would have used '*', but we already use '*' in the format string as a modifier to 'U' and 's' etc.  If someone has a better idea for the format I'd be interested.  Martin suggested using '|' a second time but I am unsure.

(Re: no reitveld link: my repo must have drifted too far and the patch didn't align cleanly.  I've freshened and am rerunning the regression test; once that runs clean I'll upload a fresh patch.)