Let ObjectDatabase implement AutoClosable

Bug: 549777
Change-Id: I09846a0e063aafa77de7e76dbc16c6a67d13b5e5

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

@@ -21,7 +21,7 @@
  * An object database stores one or more Git objects, indexed by their unique
  * {@link org.eclipse.jgit.lib.ObjectId}.
  */
-public abstract class ObjectDatabase {
+public abstract class ObjectDatabase implements AutoCloseable {
 	/**
 	 * Initialize a new database instance for access.
 	 */
@@ -74,6 +74,7 @@ public void create() throws IOException {
 	/**
 	 * Close any resources held by this database.
 	 */
+	@Override
 	public abstract void close();
 
 	/**