Created attachment 181706 [details] [review]
Enhance fallback mode as we have in ubuntu

Hey,

So, I wrote a fallback message mode before Alexandre started working on it. So yeah, there are some duplicated work there (my fault to not have push the patch sooner, but I incrementally get new functionalities to it), but not a worry :)

But I think part of the functionalities of that patch can be interested to get upstream, I'm happy to rework it against the later version for the next GNOME release.
So, basically, what we currently have in ubuntu is:
- optional and multiple fallback supports. For instance, unity can fallback to unity-2d (if installed) or gnome classic
This is done by replacing  FallbackSession by FallbackSessionsID=SessionFoo;SessionBar
Then, it will look for a SessionFoo= key in the .session file as the first fallback, test it, if doesn't exist, it will try SessionBar and so on…
- corresponding to that, there is an optional fallback message. Which means, the fallback is in the .session file:

It's basically the KeyId_Message, like:
SessionBar_Message=My fallback message.

The fallback message isn't printed if not present.

The patch also contained a force_fallback_message gconf key (can be change to gsettings for GNOME 3) to force displaying the message everytime (and engage the user to change his user session in gdm).

So the patch won't apply to the current trunk, I just want to see if some of that is desired upstream?