fix a bug

--HG--
branch : trunk

py/_com.py

@@ -90,9 +90,7 @@ class Registry:
         l = []
         if plugins is None:
             plugins = self._plugins
-        if extra:
-            plugins += list(extra)
-        for plugin in plugins:
+        for plugin in list(plugins) + list(extra):
             try:
                 l.append(getattr(plugin, attrname))
             except AttributeError:

py/misc/testing/test_com.py

@@ -135,6 +135,12 @@ class TestRegistry:
         l = list(plugins.listattr('x', reverse=True))
         assert l == [43, 42, 41]
 
+        class api4: 
+            x = 44
+        l = list(plugins.listattr('x', extra=(api4,)))
+        assert l == range(41, 45)
+        assert len(list(plugins)) == 3  # otherwise extra added
+
 def test_api_and_defaults():
     assert isinstance(py._com.comregistry, Registry)