INT-2475 Fix WS Gateway Result Payload

Fixed the return value of a non-SOAP message to return the extracted result as is, added tests

INT-2475 polishing based on PR comments

INT-2475 added POX tests for DomSource and Document as per PR suggestion

spring-integration-ws/src/main/java/org/springframework/integration/ws/AbstractWebServiceOutboundGateway.java

@@ -237,7 +237,7 @@ public abstract class AbstractWebServiceOutboundGateway extends AbstractReplyPro
 				return siMessage;
 			}
 			else {
-				return message.getPayloadSource();
+				return resultObject;
 			}
 		}