Add back the error of missing input detection.

theano/scan_module/scan_op.py

@@ -207,6 +207,10 @@ class Scan(PureOp):
         if self.info['gpu'] or self.info['gpua']:
             self._hash_inner_graph = self.info['gpu_hash']
         else:
+            # gof don't know about SharedVariable. So add them as inputs.
+            for var in theano.gof.graph.inputs(self.outputs, self.inputs):
+                if var not in self.inputs and not isinstance(var, theano.Constant):
+                    raise theano.gof.MissingInputError("ScanOp is missing an input.")
             self._cmodule_key = gof.CLinker().cmodule_key_variables(self.inputs,
                                                                     self.outputs,
                                                                     [])