glapi: use new-style Python classes.

glapi: use new-style Python classes.

An unfortunate quirk of Python 2 is that there are two types of
classes: "classic" classes (which are backward compatible with some
unfortunate design decisions made early in Python's history), and
"new-style" classes.  Classic classes have a number of limitations
(for example they don't support super()) and are unavailable in Python
3.  There's really no reason to use classic classes, except in
unmaintained legacy code.  For more information see
http://www.python.org/download/releases/2.2.3/descrintro/.

This patch upgrades the Python code in src/mapi/glapi/gen to use
exclusively new-style classes.

Tested-by: Matt Turner <mattst88@gmail.com>
Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>