Backport of a fix for the __loader__.get_data() test.

Lib/test/test_doctest.py

@@ -1912,6 +1912,7 @@ def test_DocFileSuite():
        provided.
 
          >>> import unittest, pkgutil, test
+         >>> added_loader = False
          >>> if not hasattr(test, '__loader__'):
          ...     test.__loader__ = pkgutil.get_loader(test)
          ...     added_loader = True