Use try-with-resources to fix warnings in AddCommand

- replaces use of deprecated ObjectInserter.release()
- auto-close TreeWalk

Change-Id: I540ee711b8c3430a71fdff07add506b7d9c039dc
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>

org.eclipse.jgit/src/org/eclipse/jgit/api/AddCommand.java

@@ -137,13 +137,12 @@ public class AddCommand extends GitCommand<DirCache> {
 		if (filepatterns.contains(".")) //$NON-NLS-1$
 			addAll = true;
 
-		ObjectInserter inserter = repo.newObjectInserter();
-		try {
+		try (ObjectInserter inserter = repo.newObjectInserter();
+				final TreeWalk tw = new TreeWalk(repo)) {
 			dc = repo.lockDirCache();
 			DirCacheIterator c;
 
 			DirCacheBuilder builder = dc.builder();
-			final TreeWalk tw = new TreeWalk(repo);
 			tw.addTree(new DirCacheBuildIterator(builder));
 			if (workingTreeIterator == null)
 				workingTreeIterator = new FileTreeIterator(repo);
@@ -212,7 +211,6 @@ public class AddCommand extends GitCommand<DirCache> {
 			throw new JGitInternalException(
 					JGitText.get().exceptionCaughtDuringExecutionOfAddCommand, e);
 		} finally {
-			inserter.release();
 			if (dc != null)
 				dc.unlock();
 		}