Backout RevObject's object-identity based equals implementation

This restores the transitivity and symmetry properties of the equals
methods on the AnyObjectId type hierarchy as defined in [1]. 
Following [2] we declare these equals methods final to ensure that 
semantics of equals are consistent across AnyObjectId's type hierarchy.

[1] http://download-llnw.oracle.com/javase/6/docs/api/java/lang/Object.html#equals(java.lang.Object)
[2] http://www.angelikalanger.com/Articles/JavaSolutions/SecretsOfEquals/Equals.html

Bug: 321502
Change-Id: Ibace21fa268c4aa15da6c65d42eb705ab1aa24b3
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>

org.eclipse.jgit.test/tst/org/eclipse/jgit/revwalk/RevObjectTest.java

@@ -52,7 +52,7 @@ public class RevObjectTest extends RevWalkTestCase {
 		assertSame(a, a.getId());
 	}
 
-	public void testEqualsIsIdentity() throws Exception {
+	public void testEquals() throws Exception {
 		final RevCommit a1 = commit();
 		final RevCommit b1 = commit();
 
@@ -60,8 +60,8 @@ public class RevObjectTest extends RevWalkTestCase {
 		assertTrue(a1.equals((Object) a1));
 		assertFalse(a1.equals(b1));
 
-		assertFalse(a1.equals(a1.copy()));
-		assertFalse(a1.equals((Object) a1.copy()));
+		assertTrue(a1.equals(a1.copy()));
+		assertTrue(a1.equals((Object) a1.copy()));
 		assertFalse(a1.equals(""));
 
 		final RevWalk rw2 = new RevWalk(db);
@@ -70,8 +70,8 @@ public class RevObjectTest extends RevWalkTestCase {
 		assertNotSame(a1, a2);
 		assertNotSame(b1, b2);
 
-		assertFalse(a1.equals(a2));
-		assertFalse(b1.equals(b2));
+		assertTrue(a1.equals(a2));
+		assertTrue(b1.equals(b2));
 
 		assertEquals(a1.hashCode(), a2.hashCode());
 		assertEquals(b1.hashCode(), b2.hashCode());

org.eclipse.jgit/src/org/eclipse/jgit/lib/AnyObjectId.java

@@ -230,11 +230,11 @@ public abstract class AnyObjectId implements Comparable {
 	 *            the other id to compare to. May be null.
 	 * @return true only if both ObjectIds have identical bits.
 	 */
-	public boolean equals(final AnyObjectId other) {
+	public final boolean equals(final AnyObjectId other) {
 		return other != null ? equals(this, other) : false;
 	}
 
-	public boolean equals(final Object o) {
+	public final boolean equals(final Object o) {
 		if (o instanceof AnyObjectId)
 			return equals((AnyObjectId) o);
 		else

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

@@ -96,16 +96,6 @@ public abstract class RevObject extends ObjectId {
 		return this;
 	}
 
-	@Override
-	public final boolean equals(final AnyObjectId o) {
-		return this == o;
-	}
-
-	@Override
-	public final boolean equals(final Object o) {
-		return this == o;
-	}
-
 	/**
 	 * Test to see if the flag has been set on this object.
 	 *