Fixed dummy runTest on functional test case.

In functional doc tests you can apparently have a test case that has
no runTest method.  Until now the Testing package added a dummy
runTest method in that case, and set it to None.

The previous commit added a functional test case.  Somehow this caused
a problem in an unknown other functional test case because the dummy
runTest method got called:

  Error in test runTest (Testing.ZopeTestCase.ZopeTestCase.FunctionalTestCase)
  Traceback (most recent call last):
    File ".../lib/python2.7/unittest/case.py", line 329, in run
      testMethod()
  TypeError: 'NoneType' object is not callable

It was not even caused by anything in the new tests: simply importing
was enough to trigger it:

  from Testing.ZopeTestCase import FunctionalTestCase

So this has something to do with the order in which tests are found.

I fixed it by making the dummy runTest method callable.

src/Testing/ZopeTestCase/zopedoctest/functional.py

@@ -237,8 +237,9 @@ def setup_test_class(self):
 
         # If the test_class does not have a runTest method, we add
         # a dummy attribute so that TestCase construction works.
+        # runTest may get called, so set it to something that works.
         if not hasattr(test_class, 'runTest'):
-            setattr(test_class, 'runTest', None)
+            setattr(test_class, 'runTest', lambda x: None)
 
         # Create a TestCase instance which will be used to execute
         # the setUp and tearDown methods, as well as be passed into
@@ -336,4 +337,3 @@ def FunctionalDocFileSuite(*paths, **kw):
     'FunctionalDocTestSuite',
     'FunctionalDocFileSuite',
     ]
-