Merge fix for formatting of 'extension not found' messages.

dulwich/tests/utils.py

@@ -159,7 +159,7 @@ def ext_functest_builder(method, func):
 
     def do_test(self):
         if not isinstance(func, types.BuiltinFunctionType):
-            raise SkipTest("%s extension not found", func.func_name)
+            raise SkipTest("%s extension not found" % func.func_name)
         method(self, func)
 
     return do_test