Make the readonly file just have usernames, not messages.

sagenb/notebook/notebook.py

@@ -303,8 +303,7 @@ def readonly_user(self, username):
         """
         Returns True if the user is supposed to only be a read-only user.
         """
-        readonly, message = self.__storage.readonly_user(username)
-        return readonly
+        return self.__storage.readonly_user(username)
 
     ##########################################################
     # Publishing worksheets

sagenb/storage/filesystem_storage.py

@@ -611,20 +611,17 @@ def worksheets(self, username):
 
     def readonly_user(self, username):
         """
-        Each line of the readonly file has format ``username:message``, where message could just be blank.  The colon is important.
+        Each line of the readonly file has a username.
         """
         filename = os.path.join(self._path, self._readonly_filename)
         if not os.path.exists(filename):
             return False, ''
         mtime = os.path.getmtime(filename)
         if mtime > self._readonly_mtime:
             with open(filename) as f:
-                self._readonly = dict(line[:-1].split(':',1) for line in f)
+                self._readonly = set(line[:-1] for line in f if len(line[:-1])>0)
             self._readonly_mtime = mtime
-        if username in self._readonly:
-            return True, self._readonly[username]
-        else:
-            return False, ''
+        return username in self._readonly
 
     def delete(self):
         """