simplified named_notebook_path implementation

Also updated the tests

IPython/html/services/notebooks/nbmanager.py

@@ -54,27 +54,19 b' class NotebookManager(LoggingConfigurable):'
         Returns
         -------
         name : string or None
-            the filename of the notebook, or None if not a .ipynb extesnsion
-        path : string or None
+            the filename of the notebook, or None if not a .ipynb extension
+        path : string
             the path to the directory which contains the notebook
         """
         names = notebook_path.split('/')
-        if len(names) > 1:
+
             name = names[-1]
             if name.endswith(".ipynb"):
                 name = name
-                path = notebook_path[:-1]+'/'
-            else:
-                name = None
-                path = notebook_path+'/'
-        else:
-            name = names[0]
-            if name.endswith(".ipynb"):
-                name = name
-                path = None
+            path = "/".join(names[:-1]) + '/'
             else:
                 name = None
-                path = notebook_path+'/'
+            path = "/".join(names) + '/'
         return name, path
     
     def url_encode(self, path):

IPython/html/services/notebooks/tests/test_nbmanager.py

@@ -41,9 +41,16 b' class TestNotebookManager(TestCase):'
         self.assertEqual(name, None)
         self.assertEqual(path, 'hello/')
 
+        name, path = nm.named_notebook_path('/')
+        self.assertEqual(name, None)
+
         name, path = nm.named_notebook_path('hello.ipynb')
         self.assertEqual(name, 'hello.ipynb')
-        self.assertEqual(path, None)
+        self.assertEqual(path, '/')
+        
+        name, path = nm.named_notebook_path('/hello.ipynb')
+        self.assertEqual(name, 'hello.ipynb')
+        self.assertEqual(path, '/')
         
         name, path = nm.named_notebook_path('/this/is/a/path/hello.ipynb')
         self.assertEqual(name, 'hello.ipynb')