Document protected members of RevObjectList

Recently Eclipse started complaining about undocumented protected
members here, so lets document them to make the errors go away.

Change-Id: Ia3bc9fa69854953db5dc9a982821a2f3abe8d05a
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>

org.eclipse.jgit/src/org/eclipse/jgit/revwalk/RevObjectList.java

 /*
+ * Copyright (C) 2009, Google Inc.
  * Copyright (C) 2009, Jonas Fonseca <fonseca@diku.dk>
  * Copyright (C) 2008, Shawn O. Pearce <spearce@spearce.org>
  * and other copyright owners as documented in the project's IP log.
@@ -57,12 +58,21 @@ public class RevObjectList<E extends RevObject> extends AbstractList<E> {
 
 	static final int BLOCK_SIZE = 1 << BLOCK_SHIFT;
 
+	/**
+	 * Items stored in this list.
+	 * <p>
+	 * If {@link Block#shift} = 0 this block holds the list elements; otherwise
+	 * it holds pointers to other {@link Block} instances which use a shift that
+	 * is {@link #BLOCK_SHIFT} smaller.
+	 */
 	protected Block contents = new Block(0);
 
+	/** Current number of elements in the list. */
 	protected int size = 0;
 
 	/** Create an empty object list. */
 	public RevObjectList() {
+		// Initialized above.
 	}
 
 	public void add(final int index, final E element) {
@@ -113,6 +123,7 @@ public void clear() {
 		size = 0;
 	}
 
+	/** One level of contents, either an intermediate level or a leaf level. */
 	protected static class Block {
 		final Object[] contents = new Object[BLOCK_SIZE];