Repository: Make #exactRef and #findRef final

This means less cognitive overhead for both implementors and callers,
since this way we can guarantee that they are always synonyms for
RefDatabase#exactRef and RefDatabase#findRef, respectively.

Change-Id: Ic8aeb52fc7ed65672f3f6cd1da39a66908d88baa
Signed-off-by: David Pursehouse <david.pursehouse@gmail.com>

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

@@ -1067,7 +1067,7 @@ public abstract class Repository implements AutoCloseable {
 	 * @since 4.2
 	 */
 	@Nullable
-	public Ref exactRef(String name) throws IOException {
+	public final Ref exactRef(String name) throws IOException {
 		return getRefDatabase().exactRef(name);
 	}
 
@@ -1083,7 +1083,7 @@ public abstract class Repository implements AutoCloseable {
 	 * @since 4.2
 	 */
 	@Nullable
-	public Ref findRef(String name) throws IOException {
+	public final Ref findRef(String name) throws IOException {
 		return getRefDatabase().getRef(name);
 	}