threaded IPython shell incompatible with matplotlib figures

Assuming IPython is installed, start one of the demos with --shell --debugTiming, and close the window using the q key.

Doesn't have a problem in the non-IPython threaded shell; doesn't have a problem if you close the World by quitting the IPython shell. It's only when you use the q key or otherwise call w.Close() while IPython is still running. Must be to do with the way IPython hijacks the matplotlib thread.