The tests use '#!/usr/bin/env python' which may be Python 3. Adjust the
tests to work under either Python 2 or Python 3.
This introduces a use of b"" string literals, which are supported by
Python 2.7 and Python 3, but not by Python 2.6.
Also, document the required minimum Python version.
In addition to the conversion to Python, run_all now defaults to running
all Python tests in parallel, using the same approach previously
available via '--fast'. If desired one can force all tests to run
serially by calling run_all with --serial
A debugging flag was now also included in run_all. Pass one or more -l
(-l, -ll or -lll) for different levels of debugging information.
