Editor: Disabled depthTest to selectionBox.

editor/js/ui/Viewport.js

@@ -29,6 +29,8 @@ var Viewport = function ( signals ) {
 
 	var selectionBox = new THREE.BoxHelper();
 	selectionBox.material.color.setHex( 0xffff00 );
+	selectionBox.material.depthTest = false;
+	selectionBox.material.transparent = true;
 	selectionBox.visible = false;
 	sceneHelpers.add( selectionBox );