Auto show Overview when workspace is empty

[clemens <clemens lab21 org>]

hi, 

i have a two screen setup and use keyboard bindings to move windows
between my screens. This works quite good but when only one window
exists on the current workspace and i move it from primary to secondary
monitor, the overview is shown.

* If i move the window using the keyboard, the overview is shown. The
extension moves the window using:
 > win.move_frame(true, x - padding.x, y - padding.y);

* If i move the window to second screen using the mouse, the overview is
not shown. But is looks like the workspace is removed and recreated
immediately. (the windows from the workspace above is shown very short)

Can i achieve a similar behaviour (dont show overview) when moving the
window with my extension? 

thanks in advance, 
  clemens

(using gnome-shell 3.2.1)