Whenever client.focus == nil, we set the input focus to the root window to
express "nothing has the input focus". However, thanks to the way X11 input
works, this means that whatever is under the mouse cursor gets keyboard input
events. This can easily be reproduced with urxvt and some small addition to the
config to unfocus things.
This commit changes things. Instead of focusing the root window, we create a
special "no focus" window that gets focused if we want nothing to have the
focus.
Closes https://github.com/awesomeWM/awesome/pull/470.
Signed-off-by: Uli Schlachter <psychon@znc.in>