Python test runner features

I have some features to add to run-tests.py.  I haven't filed an issue for this because it's infrastructural feature work and also not exactly *done* yet -- I have several more changes in mind -- but I want to make you aware of it now, particularly the changes to the TESTS array and the embedded HTTP server, which will help us collectively not step on each others' toes while converting tests.  Please see individual commits for explanations.