make error more clear that the user can ignore it.

theano/tensor/opt.py

@@ -3102,9 +3102,10 @@ def local_elemwise_fusion_op(OP, max_input_fct=lambda node: 1024):
         if not fused:
             return False
 
-        if new_nb_input != len(inputs):
-            raise Exception("Something has gone wrong with the elemwise fusion optimization.")
-        assert len(s_inputs) == len(inputs)
+        if new_nb_input != len(inputs) or len(s_inputs) != len(inputs):
+            raise Exception("""Something has gone wrong with the elemwise
+fusion optimization. We skip this optimization. You can ignore this message,
+your code will run correctly, but maybe slower.""")
 
         otype = node.outputs[0].type
         s_new_out=node.op.scalar_op(*s_g)