Enable v_y in caret mode. Closes issue #685.

common/modules/buffer.jsm

@@ -557,6 +557,11 @@ var Buffer = Module("Buffer", {
                          0);
     },
 
+    /**
+     * @property {nsISelection} The current document's normal selection.
+     */
+    get selection() this.win.getSelection(),
+
     /**
      * @property {nsISelectionController} The current document's selection
      *     controller.