Bugfix: moving across outputs sends IPC event

Long description:

When moving a container across output with `move <direction>`, send the
IPC workspace focus event with `workspace_show` so that i3bar updates
correctly.

To apply this patch, use:
curl http://cr.i3wm.org/patch/365/raw.patch | git am

@@ -71,6 +71,7 @@ static void insert_con_into(Con *con, Con *target, position_t position) {

  *

  */

 static void attach_to_workspace(Con *con, Con *ws, direction_t direction) {

+    Con *old_ws = con_get_workspace(con);

     con_detach(con);

     con_fix_percent(con->parent);

@@ -91,6 +92,10 @@ static void attach_to_workspace(Con *con, Con *ws, direction_t direction) {

      * does not make sense anyways. */

     con->percent = 0.0;

     con_fix_percent(ws);

+

+    /* We do our best to get the IPC event right */

+    con_focus(old_ws);

+    workspace_show(ws);

 }

 /*