Replaced the test case hierarchy schema with a vector version.

The OmniGraffle source file is included for future use.

docs/topics/http/middleware.txt

@@ -65,8 +65,8 @@ reverse order, from the bottom up. Three hooks are available:
 
 .. image:: _images/middleware.*
    :alt: middleware application order
-   :width: 480
-   :height: 408
+   :width: 481
+   :height: 409
 
 If you prefer, you can also think of it like an onion: each middleware class
 is a "layer" that wraps the view.

docs/topics/testing.txt

@@ -1186,10 +1186,13 @@ Normal Python unit test classes extend a base class of
 
 .. _testcase_hierarchy_diagram:
 
-.. figure:: _images/django_unittest_classes_hierarchy.png
+.. figure:: _images/django_unittest_classes_hierarchy.*
    :alt: Hierarchy of Django unit testing classes (TestCase subclasses)
+   :width: 508
+   :height: 391
 
-   Hierarchy of Django unit testing classes
+Regardless of the version of Python you're using, if you've installed
+:mod:`unittest2`, :mod:`django.utils.unittest` will point to that library.
 
 TestCase
 ^^^^^^^^