Update pytz to 2012d and update dateutil to 1.5 for Python 2.x and 2.1 for Python 3.x

Update setup.py so that it assume datetime is always there (as it should be on the versions of Python we support).

Update setup.py to not 2to3 pytz.

Update setup.py to install the correct version of dateutil that matches the version of Python.

Author: mdboom

doc/users/whats_new.rst

@@ -127,6 +127,16 @@ local intensity of the vector field.
 
 .. plot:: mpl_examples/pylab_examples/streamplot_demo.py
 
+Updated shipped dependencies
+----------------------------
+
+The following dependencies that ship with matplotlib and are
+optionally installed alongside it have been updated:
+
+  - `pytz <http://pytz.sf.net/>` 2012d
+
+  - `dateutil <http://labix.org/python-dateutil>` 1.5 on Python 2.x,
+    and 2.1 on Python 3.x
 
 .. _whats-new-1-1: