[XML-SIG] SAX parser factories (Was: PyTRaX?)

[Rich Salz]

I think this is pretty close. :)

I think the keyword arguments properties and features should take
dictionaries.

> There should also be a function xml.sax.register_parser, which accepts
> an object that has a create_parser function, or a string naming a
> module that has a create_parser function.

I think perhaps
	def can_create_parser(properties={}, features={}):
		'If you can create a parser with the desired properties and features,
		return non-None.  If you cannot, return None.'

	def create_parser(properties={}, features={}):
		'Create a parser with the specified prperties and features, return
		None (raise an exception?) if not possible.'

Is a little cleaner set of callbacks.