Fixed #12632 -- Improved performance of `SortedDict`. Thanks, Alex Gaynor.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@13742 bcc190cf-cafb-0310-a4f2-bffc1f526a37

django/utils/datastructures.py

@@ -120,9 +120,11 @@ class SortedDict(dict):
             self.keyOrder = data.keys()
         else:
             self.keyOrder = []
+            seen = set()
             for key, value in data:
-                if key not in self.keyOrder:
+                if key not in seen:
                     self.keyOrder.append(key)
+                    seen.add(key)
 
     def __deepcopy__(self, memo):
         return self.__class__([(key, deepcopy(value, memo))