Changed the test setup for easier sub-test running.

I was creating my own unittest.TestSuite, but this appears (from reading
the Django code) to not be necessary. Auto-discovery takes place if I
import the TestCase instances into the "acacia.tests" namespace and then
I can restrict test runs to invidivual TestCases.

acacia/tests/__init__.py

@@ -1,10 +1,4 @@
-import unittest
-
-from acacia.tests import test_models, test_templatetags
-
-def suite():
-    test_suite = unittest.defaultTestLoader.loadTestsFromModule(test_models)
-    test_suite.addTests(unittest.defaultTestLoader. \
-            loadTestsFromModule(test_templatetags))
-    return test_suite
+from acacia.tests.test_models import TopicTest
+from acacia.tests.test_templatetags import (TreeTrunkErrorTests,
+        TreeTrunkMiscTests, TreeTrunkSingleRootTests, TreeTrunkFullContentTests)