OverlayW3CDOMStreamWriter is not allowing multiple elements of the same name to be written out

When using a Provider<SOAPMessage>, and schema validation is turned on, the body contents are written to the OverlayW3CDOMStreamWriter. If the contents have two elements at the same level (maxOccurs != 1 type thing), they end up merged together.

There is a "side" optimization in that with Provider<SOAPMessage>, we shouldn't need to buffer the out since it's a DOM already.