fallback and safe modes

[Rahul Sundaram]

Hi

If for some reason, fallback mode doesn' get activated or the default
interface is not working properly, would it be useful to have a option
to choose fallback mode in GDM itself?  I recently ran into a issue
where GNOME Shell would launch but all the windows were black and hence
couldn't go to system settings and force fallback mode on.  I traced
this problem due a upgrade issue eventually but in such situations,
ability to choose the mode right in the login screen is useful

Another option I think is needed is a safe mode which basically ignores
all the installed extensions.  The reason is that, these GNOME Shell
extensions are essentially arbitrary javascript and if I install a bunch
of extensions and one of them has a bug, GNOME Shell basically gives up
and you can't login.  Similar to Firefox, a safe mode might be handy to have

Rahul