Have git-ls tree to accept path args like git-ls-tree

Usage is:

jgit ls-tree [-r|--recursive] <tree-ish> [-- paths...]

Change-Id: I2e1c9c3cc8cddfa12ca4bfb9afc4df0492a9fce1
Signed-off-by: Robin Rosenberg <robin.rosenberg@dewire.com>
Signed-off-by: Chris Aniszczyk <zx@twitter.com>

org.eclipse.jgit.pgm/src/org/eclipse/jgit/pgm/LsTree.java

@@ -45,12 +45,17 @@
 
 package org.eclipse.jgit.pgm;
 
-import org.kohsuke.args4j.Argument;
-import org.kohsuke.args4j.Option;
+import java.util.ArrayList;
+import java.util.List;
+
 import org.eclipse.jgit.lib.Constants;
 import org.eclipse.jgit.lib.FileMode;
 import org.eclipse.jgit.treewalk.AbstractTreeIterator;
 import org.eclipse.jgit.treewalk.TreeWalk;
+import org.eclipse.jgit.treewalk.filter.PathFilterGroup;
+import org.kohsuke.args4j.Argument;
+import org.kohsuke.args4j.Option;
+import org.kohsuke.args4j.spi.StopOptionHandler;
 
 class LsTree extends TextBuiltin {
 	@Option(name = "--recursive", usage = "usage_recurseIntoSubtrees", aliases = { "-r" })
@@ -59,9 +64,16 @@ class LsTree extends TextBuiltin {
 	@Argument(index = 0, required = true, metaVar = "metaVar_treeish")
 	private AbstractTreeIterator tree;
 
+	@Argument(index = 1)
+	@Option(name = "--", metaVar = "metaVar_paths", multiValued = true, handler = StopOptionHandler.class)
+	private List<String> paths = new ArrayList<String>();
+
 	@Override
 	protected void run() throws Exception {
 		final TreeWalk walk = new TreeWalk(db);
+		walk.reset(); // drop the first empty tree, which we do not need here
+		if (paths.size() > 0)
+			walk.setFilter(PathFilterGroup.createFromStrings(paths));
 		walk.setRecursive(recursive);
 		walk.addTree(tree);