Add Theano flag unpickle_function to work around problem with unpickle.

theano/compile/function_module.py

@@ -709,6 +709,8 @@ def _pickle_Function(f):
     return rval
 
 def _constructor_Function(maker, input_storage, inputs_data):
+    if not theano.config.unpickle_function:
+        return None
     f = maker.create(input_storage, trustme = True)
     assert len(f.input_storage) == len(inputs_data)
     for container, x in zip(f.input_storage, inputs_data):
@@ -1204,7 +1206,10 @@ def _pickle_FunctionMaker(self):
 
 
 def _constructor_FunctionMaker(kwargs):
+    if theano.config.unpickle_function:
         return FunctionMaker(**kwargs)
+    else:
+        return None
 
 copy_reg.pickle(FunctionMaker, _pickle_FunctionMaker)
 

theano/configdefaults.py

@@ -410,6 +410,13 @@ AddConfigVar('compute_test_value_opt',
              EnumStr('off', 'ignore', 'warn', 'raise', 'pdb'),
              in_c_key=False)
 
+AddConfigVar('unpickle_function',
+             ("Replace unpickled Theano function with None",
+              "This is useful to unpickle old graph that pickled"
+              " them when it shouldn't"),
+             BoolParam(True),
+             in_c_key=False)
+
 """Note to developers:
     Generally your exceptions should use an apply node's __str__
     method when exception_verbosity == 'low'. When exception_verbosity