INT-2517 - Upgrade to Spring 3.1

* Update **build.gradle** and change the *springVersion* property to **3.1.1.RELEASE**
* Due to change in Spring 3.1, add missing method **getRawStatusCode()** in *org.springframework.integration.http.outbound.CookieTests*

spring-integration-http/src/test/java/org/springframework/integration/http/outbound/CookieTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2011 the original author or authors.
+ * Copyright 2002-2012 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -50,6 +50,8 @@ import org.springframework.test.context.junit4.SpringJUnit4ClassRunner;
 
 /**
  * @author Gary Russell
+ * @author Gunnar Hillert
+ *
  * @since 2.1
  *
  */
@@ -139,6 +141,10 @@ public class CookieTests {
 
 						public void close() {
 						}
+
+						public int getRawStatusCode() throws IOException {
+							return 200;
+						}
 					};
 				}
 			};