Replace xscreensaver with lightdm builtin "gdmflexiserver"

[mard0]

By replacing xscreensaver with gdmflexiserver in xflock4 there is a more uniform desktop experience.
This can be done by replacing:
for lock_cmd in \
    "xscreensaver-command -lock" \
    "gnome-screensaver-command --lock"
do
    $lock_cmd >/dev/null 2>&1 && exit
done

With:

for lock_cmd in \
    "gdmflexiserver"
do
    $lock_cmd >/dev/null 2>&1 && exit
done

ProblemType: Bug
DistroRelease: Ubuntu 13.04
Package: xfce4-session 4.10.0-2ubuntu1 [modified: usr/bin/xflock4]
ProcVersionSignature: Ubuntu 3.8.0-14.24-generic 3.8.4
Uname: Linux 3.8.0-14-generic x86_64
NonfreeKernelModules: fglrx
ApportVersion: 2.9.2-0ubuntu3
Architecture: amd64
Date: Mon Mar 25 19:40:43 2013
MarkForUpload: True
SourcePackage: xfce4-session
UpgradeStatus: No upgrade log present (probably fresh install)

[Lionel Le Folgoc (mrpouit)]

The gdmflexiserver wrapper won't lock the screen by itself, it still requires a screenlocker (there's been ongoing work with light-locker and lightdm-gtk-greeter, but it's not ready).

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.

[Alex Mason (0k53dmx9cig8cqkasqs0vq-alex)]

This works fantastically, with the one small problem that the flexiserver allows other users to log in. Typically locking the screen means only the logged in user can unlock it. However, I support the idea that the display manager should be handling screen locks rather than xscreensaver.

[Aaron Patterson (apatters)]

For what it's worth, I think when you lock the screen on Windows you get a login prompt where anyone can log in. Same with OSX. Doesn't seem like a bad thing to me.

[Thaddaeus Tintenfisch (thad-fisch-deactivatedaccount)]

xscreensaver has been replaced by light-locker (simple session-locker for lightdm) in Xubuntu 14.04.

https://launchpad.net/light-locker