Added namespace support for http outbound-gateway (INT-616).

org.springframework.integration/src/main/java/org/springframework/integration/config/xml/AbstractConsumerEndpointParser.java

@@ -66,7 +66,7 @@ public abstract class AbstractConsumerEndpointParser extends AbstractBeanDefinit
 		if (!element.hasAttribute(inputChannelAttributeName)) {
 			if (!parserContext.isNested()) {
 				parserContext.getReaderContext().error("The '" + inputChannelAttributeName
-						+ "' attribute is required for top-level endpoint elements.", element);
+						+ "' attribute is required for this top-level endpoint element.", element);
 			}
 			return handlerBeanDefinition;
 		}