Merge pull request #1886 from tkf/fix-notebook-rename

Fix a bug in renaming notebook caused by keeping a stale reference to old names.

IPython/frontend/html/notebook/notebookmanager.py

@@ -228,6 +228,7 b' class NotebookManager(LoggingConfigurable):'
                     os.unlink(old_pypath)
             self.mapping[notebook_id] = new_name
             self.rev_mapping[new_name] = notebook_id
+            del self.rev_mapping[old_name]
 
     def delete_notebook(self, notebook_id):
         """Delete notebook by notebook_id."""