wheezy-stage4-lxde: fix gksu/gksudo problem in a more elegant way
wheezy-stage4-lxde: fix gksu/gksudo problem in a more elegant way

Rather than trying to fix everywhere that calls gksu, the proper fix is of
course to set the /apps/gksu/sudo-mode. Debian obviously already has a way of
doing this in the update-alternatives system, so let's use that.

asb/spindle,thusoy/spindle,MrNice/spindle,RPi-Distro/spindle