Bug#941640: gnome-session: Gnome 3.34 fails to start showing grey screen "Oh no, something has gone wrong")

[Drew Parsons]

More tests: the failure occurs when logging in with "System X11 Default" 
or "Gnome Classic" selected from the gdm3 login screen.

Log-in via the plain "Gnome" option does successfully start a 
gnome-session.  Extensions from 3.30 cause it to freeze, but that's a 
separate issue (it works if extensions are disabled).