(texi2html.py): Use "if __name__ == '__main__':" test. Adjust indentation

to 4 spaces per level (no longer 8).

(Makefile):  Use .pyc versions of partparse.py and texi2html.py to generate
	converted documentation formats.  This reduces the startup costs;
	probably doesn't affect anyone but me in reality, but helps when
	working on the docs.