Comment # 14 on bug 1140184 from Stakanov Schufter

FYI, the MESA_EXTENSION_OVERRIDE="-GL_ATI_fragment_shader" entry has a
secondary, positive, side effect on the plasma desktop. 

Normally since long time I was haunted by the "black screen after changing user
with alt+ctl+fn key combination. The system would stay either hanging with a
black screen (until reboot) or would enter the normal function only if entering
space bar or sometimes enter. This would take about 30 seconds, sometimes more. 

This is entirely gone with the entry as of above. So on a X201 Lenovo, this
change makes not only falkon faster, it makes also the desktop more stable.