A new window is by default above all other windows. This means that when we map
it and then *later* move it to the correct place in the stacking order (thanks
to lazy restacking), the window on the top of the stack has to redraw itself.
I noticed this via naughty notifies redrawing themselves after opening a browser
window.
Signed-off-by: Uli Schlachter <psychon@znc.in>