[gentoo-python] [PATCH] python.eclass: Avoid multiple inclusion

[Mike Gilbert]

Mike's doing it in autotools.eclass, so let's do it too.

This will aid in debugging code in global scope and prevent duplicate
dependency atoms from being generated. Also, per vapier[1], it could
have some performance enhancing qualities.

The distutils part avoids sourcing python.eclass if distutils is
inherited after python. We can add similar blocks to other eclass
consumers of python.eclass.

I think it's a good idea, and you should to.

Please see attached patch. Please let me know you have some objection;
otherwise I will commit on Sunday, Jan 1.

[1]
http://archives.gentoo.org/gentoo-dev/msg_18dab542c1c59873f8cb68c96cdf6619.xml