mercurial/extensions.py

--- a/mercurial/extensions.py	Tue Feb 02 21:20:04 2016 -0800
+++ b/mercurial/extensions.py	Fri Feb 05 13:20:23 2016 +0100
@@ -468,3 +468,7 @@
     if isinstance(version, (list, tuple)):
         version = '.'.join(str(o) for o in version)
     return version
+
+def ismoduleinternal(module):
+    exttestedwith = getattr(module, 'testedwith', None)
+    return exttestedwith == "internal"