Request/response element pairs.

In today's conference call, Rami suggested that each request element 
should have a corresponding response element for reasons of clarity.  
During the conference call, Jeff Bohren objected that defining a new 
type (e.g., BulkModifyResponseType that extends spml:ResponseType but 
adds nothing) would be overkill.

However, it occurs to me that we could add a new top-level element 
without defining a new type. 

For example, in the bulk capability where it declares:   
   <element name="bulkDeleteRequest" 
type="spmlbulk:BulkDeleteRequestType" />
we could add:
   <element name="bulkDeleteResponse" type="spml:ResponseType" />

I believe that this would meet Rami's goals without defining an 
unnecessary type.

Gary