Update six.py to version 1.2

[cgohlke]

http://pypi.python.org/pypi/six/

[pelson]

Including this package at the top level is bad practice in my eyes. It is going to conflict with other people's installation of six. I can see why we want to package it with mpl, but was there a reason not to put it under a sub-package of matplotlib? matplotlib.compatibility.six for instance...

[mdboom]

As per a longing-standing practice with dependencies in matplotlib, it is only installed if it isn't already there. It was not installed as a subpackage because that would require patching dateutil to use it as a subpackage instead of at the top-level, which is even more of a maintenance burden.

I have remained with this approach for 1.2.x because there are many (including at my institution) who depend on these dependencies being included. However, for a not-too-far-off release, we should really get pip automatic dependency downloading working better. This is in bug #1157.

[pelson]

Thanks for a full response on that. I take your points and agree with your sentiments.