INT-4506: Splitter: close stream and Closeables

JIRA: https://jira.spring.io/browse/INT-4506

Capture the actual splitter result in the `FunctionIterator and close it if necessary.

**cherry-pick to 5.0.x**

Add Closeable to proxy in test; remove AutoCloseable check.

Closeable extends AutoCloseable.

Fix javadocs; test for AutoCloseable instead of Closeable

Polishing - PR comments; tighten up API.

A `CloseableIterator` is now an `AutoCloseable` with an overridden
`close()`` (no exception) to avoid lint problem.

* Polishing omissions, code style and `@author`

**Cherry-pick to 5.0.x**

(cherry picked from commit bebde26)

spring-integration-xml/src/main/java/org/springframework/integration/xml/splitter/XPathMessageSplitter.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2017 the original author or authors.
+ * Copyright 2002-2018 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.
@@ -329,7 +329,7 @@ public class XPathMessageSplitter extends AbstractMessageSplitter {
 
 		TransformFunctionIterator(Iterator<Node> delegate,
 				Function<? super Node, ? extends String> function) {
-			super(delegate, function);
+			super(null, delegate, function);
 			this.delegate = delegate;
 		}