Made django.test.testcases not depend on staticfiles contrib app.

Do this by introducing a django.contrib.staticfiles.testing.StaticLiveServerCase
unittest TestCase subclass.

Fixes #20739.

docs/releases/1.7.txt

@@ -332,6 +332,20 @@ Miscellaneous
   Define a ``get_absolute_url()`` method on your own custom user object or use
   :setting:`ABSOLUTE_URL_OVERRIDES` if you want a URL for your user.
 
+* The static asset-serving functionality of the
+  :class:`django.test.LiveServerTestCase` class has been simplified: Now it's
+  only able to serve content already present in :setting:`STATIC_ROOT` when
+  tests are run. The ability to transparently serve all the static assets
+  (similarly to what one gets with :setting:`DEBUG = True <DEBUG>` at
+  development-time) has been moved to a new class that lives in the
+  ``staticfiles`` application (the one actually in charge of such feature):
+  :class:`django.contrib.staticfiles.testing.StaticLiveServerCase`. In other
+  words, ``LiveServerTestCase`` itself is less powerful but at the same time
+  has less magic.
+
+  Rationale behind this is removal of dependency of non-contrib code on
+  contrib applications.
+
 Features deprecated in 1.7
 ==========================