More explicit error message

gof/env.py

@@ -136,7 +136,7 @@ class Env(utils.object2):
                     if hasattr(r, 'env') and r.env is not self:
                         raise Exception("%s is already owned by another env" % r)
                     if r.owner is None and not isinstance(r, graph.Value) and r not in self.inputs:
-                        raise TypeError("Undeclared input", r)
+                        raise TypeError("An input of the graph was not provided and not given a value", r)
         
         for node in new_nodes:
             self.__setup_node__(node)