Increase z-index for undo tooltip

When interface language selector is at the top, the undo tooltip
may appear under new Vector search box and other user tool links.

Change-Id: I36ac01511e590896afb0382c17ae90d01ba57314

resources/css/ext.uls.interface.less

@@ -35,3 +35,7 @@
 		}
 	}
 }
+
+.uls-tipsy.uls-tipsy {
+	z-index: 1000;
+}