Bug#1016004: lightdm: re-login possible without password after "dm-tool lock"

[HG <hg_code@gmx.de>]

Thank you for your explanations, Yves-Alexis.

I have now tried what you suggested:
* I installed light-locker (1.8.0-3)
* restarted the OS
* typed "dm-tool lock" into a console
* result: the screen is perfectly locked.
So once light-locker is installed, the screen locking works perfectly well and my "buggy" behavior described previoulsy, is gone.

Still, I would like to try to improve the situation here. Two ideas come to my mind:

1. When I type "dm-tool lock", before installing light-locker package at all, I do not get an error message. The software just silently fails to do the requested and security relevant action. Would it  be possible to at least issue an error message (on the console at least) from dm-tool when screen locking is requested but no screen locking software is installed?

2. Would it be reasonably possible to introduce some package dependendies to avoid that dummy users (like me) get into this trouble? Could maybe the package "light-locker" be a (at least recommended) package dependency of the package "lightdm" (including the dm-tool command)? Would this generate other trouble or might this be a feasible improvement?