Only show logout button if logged in.

IPython/frontend/html/notebook/handlers.py

@@ -182,7 +182,10 class LoginHandler(AuthenticatedHandler):
         )
 
     def get(self):
-        self._render()
+        if self.current_user:
+            self.redirect(self.get_argument('next', default='/'))
+        else:
+            self._render()
 
     def post(self):
         pwd = self.get_argument('password', default=u'')

IPython/frontend/html/notebook/templates/layout.html

@@ -23,7 +23,9
 <div id="header">
     <span id="ipython_notebook"><h1>IPython Notebook</h1></span>
     <span id="login_widget">
-      <button id="logout">Logout</button>
+      {% if current_user and current_user != 'anonymous' %}
+        <button id="logout">Logout</button>
+      {% end %}
     </span>
     {% block header %}
     {% end %}