Description:
if i'm interpreting this correctly, the current virtualbox-guest-additions gives xorg opengl software (softpipe) rendering, even if "3D acceleration" is activated in virtualbox host app.

attached is an untested patch, that at least works here when doing the symlink manually...

Additional info:
* community/virtualbox-guest-additions 4.0.6-1
* community/virtualbox 4.0.6-1
(my host has nvidia binary drivers on gtx460, if that even matters)

Steps to reproduce:
install arch as guest
install "xorg" and mesa-demos
install virtualbox-guest-additions
load the vbox* modules
startx

see what `glxinfo | grep -i opengl` gives:
OpenGL vendor string: VMware, Inc.
OpenGL renderer string: Gallium 0.4 on softpipe
OpenGL version string: 2.1 Mesa 7.10.2
OpenGL shading language version string: 1.20
OpenGL extensions:

the attached patch should give:
OpenGL vendor string: Humper
OpenGL renderer string: Chromium
OpenGL version string: 2.1 Chromium 1.9
OpenGL shading language version string: 4.10 NVIDIA via Cg compiler
OpenGL extensions:

Reference:
http://www.virtualbox.org/ticket/7194