Use rpartition here, essential to the algorithm. Fixes #259.

--HG--
extra : amend_source : d7b3c001b4db616a67793dcc57d5c13e3828ad3a

setuptools/command/install_lib.py

@@ -43,7 +43,7 @@ class install_lib(orig.install_lib):
         """
         while pkg_name:
             yield pkg_name
-            pkg_name, sep, child = pkg_name.partition('.')
+            pkg_name, sep, child = pkg_name.rpartition('.')
 
     def _get_SVEM_NSPs(self):
         """