Bug#804139: bumblebee: after recent xorg + nvidia updates in sid, "Cannot access secondary GPU - error"

[Debian stuff]

Finishing December, I'm still suffering the same problem since that
update. Maybe it has something to do with the new Xorg being run on
userspace?

I add my information because it contains logs from bumblebee:

    $ sudo systemctl status bumblebeed
    ● bumblebeed.service - Bumblebee C Daemon
       Loaded: loaded (/lib/systemd/system/bumblebeed.service; enabled;
vendor preset: enabled)
       Active: active (running) since mié 2015-12-30 09:30:34 CET;
20min ago
     Main PID: 875 (bumblebeed)
       CGroup: /system.slice/bumblebeed.service
               └─875 /usr/sbin/bumblebeed

    dic 30 09:30:34 arepa systemd[1]: Started Bumblebee C Daemon.
    dic 30 09:31:47 arepa bumblebeed[875]: [   96.854001]
[INFO]/usr/sbin/bumblebeed 3.2.1 started

    $ optirun -vv glxgears
    [ 1316.366496] [DEBUG]Reading file: /etc/bumblebee/bumblebee.conf
    [ 1316.367218] [DEBUG]optirun version 3.2.1 starting...
    [ 1316.367276] [DEBUG]Active configuration:
    [ 1316.367297] [DEBUG] bumblebeed config file:
/etc/bumblebee/bumblebee.conf
    [ 1316.367316] [DEBUG] X display: :8
    [ 1316.367335] [DEBUG] LD_LIBRARY_PATH: /usr/lib/x86_64-linux-
gnu/nvidia:/usr/lib/i386-linux-gnu/nvidia:/usr/lib/nvidia
    [ 1316.367354] [DEBUG] Socket path: /var/run/bumblebee.socket
    [ 1316.367372] [DEBUG] Accel/display bridge: auto
    [ 1316.367390] [DEBUG] VGL Compression: proxy
    [ 1316.367408] [DEBUG] VGLrun extra options:
    [ 1316.367426] [DEBUG] Primus LD Path: /usr/lib/x86_64-linux-
gnu/primus:/usr/lib/i386-linux-
gnu/primus:/usr/lib/primus:/usr/lib32/primus
    [ 1316.367564] [DEBUG]Using auto-detected bridge primus
    [ 1316.374559] [INFO]Response: No - error: [XORG] (EE)

    [ 1316.374600] [ERROR]Cannot access secondary GPU - error: [XORG]
(EE)

    [ 1316.374620] [DEBUG]Socket closed.
    [ 1316.374649] [ERROR]Aborting because fallback start is disabled.
    [ 1316.374672] [DEBUG]Killing all remaining processes.

    $ sudo systemctl status bumblebeed
    ● bumblebeed.service - Bumblebee C Daemon
       Loaded: loaded (/lib/systemd/system/bumblebeed.service; enabled;
vendor preset: enabled)
       Active: active (running) since mié 2015-12-30 09:30:34 CET;
22min ago
     Main PID: 875 (bumblebeed)
       CGroup: /system.slice/bumblebeed.service
               └─875 /usr/sbin/bumblebeed

    dic 30 09:52:07 arepa bumblebeed[875]: [ 1316.374416] [ERROR][XORG]
(EE)
    dic 30 09:52:07 arepa bumblebeed[875]: [ 1316.374445] [ERROR][XORG]
(EE)
    dic 30 09:52:07 arepa bumblebeed[875]: [ 1316.374452] [ERROR][XORG]
(EE)
    dic 30 09:52:07 arepa bumblebeed[875]: [ 1316.374456] [ERROR][XORG]
(EE)
    dic 30 09:52:07 arepa bumblebeed[875]: [ 1316.374461] [ERROR][XORG]
(EE)
    dic 30 09:52:07 arepa bumblebeed[875]: [ 1316.374465] [ERROR]X did
not start properly