Use the DefaultOrderedDict for all optimizer DB.

theano/gof/optdb.py

 import StringIO
 import sys
 
-if sys.version_info[:2] >= (2, 5):
-    from collections import defaultdict
-else:
-    from python25 import defaultdict
+from python25 import DefaultOrderedDict
 
 import numpy
 import opt
@@ -29,7 +26,7 @@ class DB(object):
         return self._optimizer_idx
 
     def __init__(self):
-        self.__db__ = defaultdict(set)
+        self.__db__ = DefaultOrderedDict(set)
         self._names = set()
         self.name = None  # will be reset by register
         #(via obj.name by the thing doing the registering)