"Oh no!" / Xorg crash after logging in at the Greeter with Intel 855GM graphics

Originally created by @goupille on #11096 (Redmine)

a user reported that error, I think it is related to https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=776911 and
https://labs.riseup.net/code/issues/8778.

the user could send us the result of ‘sudo tails-debugging-info’, I found that in the logs :

Feb 08 17:32:19 localhost.localdomain kernel: [drm:i9xx_check_fifo_underruns] *ERROR* pipe B underrun
Feb 08 17:45:35 amnesia kernel: [drm:i9xx_set_fifo_underrun_reporting] *ERROR* pipe A underrun
Feb 08 17:49:25 amnesia kernel: [drm:i8xx_irq_handler] *ERROR* pipe B underrun

and

Feb 08 17:45:21 amnesia gnome-session[3791]: (gnome-shell:4839): Cogl-ERROR **: Failed to create texture 2d due to size/format constraints
Feb 08 17:45:21 amnesia x-session-manager[3791]: WARNING: Application 'gnome-shell-classic.desktop' killed by signal 5
Feb 08 17:45:21 amnesia x-session-manager[3791]: WARNING: App 'gnome-shell-classic.desktop' respawning too quickly
Feb 08 17:45:21 amnesia x-session-manager[3791]: Unrecoverable failure in required component gnome-shell-classic.desktop
Feb 08 17:45:21 amnesia gnome-session[3791]: x-session-manager[3791]: WARNING: Application 'gnome-shell-classic.desktop' killed by signal 5
Feb 08 17:45:21 amnesia gnome-session[3791]: x-session-manager[3791]: WARNING: App 'gnome-shell-classic.desktop' respawning too quickly
Feb 08 17:45:21 amnesia gnome-session[3791]: (gnome-settings-daemon:3881): GLib-GIO-CRITICAL **: g_dbus_proxy_call_internal: assertion 'G_IS_DBUS_PROXY (proxy)' failed

Feature Branch: emmapeel:doc-11096