indicator-session: "Lock" hardcoded for gnome-screensaver blocking portablity; enable a cross-platform screen locker

[quequotion]

Indicator-session calls gnome-screensaver via dbus for screen-locking; it features no configuration options to work with any other screen locking utilities. Gnome-screensaver makes for neither a good screensaver or a screen locker and offers only slightly more functionality than simply turning off the screen at a significantly higher wattage.

Indicator-session would be more useful if the locking utility were configurable, say for users who want gnome-screensaver in Ubuntu or for users who would prefer light-locker to offer more secure session locking with functional lightdm integration.

Indicator-session has some code for light-dm integration on user-switching, but to be honest i can hardly make heads or tails of that entire block of code; can't even tell you specificly where the call to org.gnome.ScreenSaver.Lock() is happening (though it definitely is happening).

After fixing bug 1354790, this would be a good followup for portability efforts.

In the mean time, in order to make indicator-session's "Lock" do something on desktops without gnome-screensaver or Unity, there is a workaround:

light-locker-dbus-screenlocker
https://github.com/quequotion/pantheon-bzr-qq/commit/e60cdd21f37c7c22723dc18befe951a7cf5d1a66

The link is to packaging for archlinux, but really this is just a simple python script (adapted from one found in the ubuntu forums that originally called xscreensaver's locker). This script emulates the dbus "Lock" function of gnome-screensaver, but activates light-locker's lightdm lockscreen.