StandardMultipartFile declares itself as Serializable now

Issue: SPR-12795
(cherry picked from commit 5ba7b89)

Author: jhoeller

spring-web/src/main/java/org/springframework/web/multipart/support/StandardMultipartHttpServletRequest.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2014 the original author or authors.
+ * Copyright 2002-2015 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.
@@ -19,6 +19,7 @@
 import java.io.File;
 import java.io.IOException;
 import java.io.InputStream;
+import java.io.Serializable;
 import java.util.ArrayList;
 import java.util.Collection;
 import java.util.Collections;
@@ -206,7 +207,8 @@ public HttpHeaders getMultipartHeaders(String paramOrFileName) {
 	/**
 	 * Spring MultipartFile adapter, wrapping a Servlet 3.0 Part object.
 	 */
-	private static class StandardMultipartFile implements MultipartFile {
+	@SuppressWarnings("serial")
+	private static class StandardMultipartFile implements MultipartFile, Serializable {
 
 		private final Part part;