Bug#922718: /usr/bin/xflock4: please support xfce4-screensaver

[Dominik George]

Hi,

>I'm not sure at all I want to actually replace lightdm/light-locker by
>xfce4-
>screensaver.

Noone requested that.

The attached patch uses xfce4-screensaver only if lightdm is not available, as 
in situations already described.

-nik