python: wvtest scripts can now be executable, like unittest scripts.

python: wvtest scripts can now be executable, like unittest scripts.

Now you can either do:
	./wvtest.py t/mytest.py
or
	python t/mytest.py

If you want to do the latter, you need lines like this at the end of
mytest.py:
	if __name__ == '__main__':
	    wvtest_main()

This makes it work more like the python standard unittest library, and makes
it really obvious how to run any given test file from the command line,
independent from the others.