Find-rendering-devices-code in masterjob now peeks into /tmp/.X11-unix
to locate all X servers, and then iterates over these to find which
screens that are accessible. This is propagated into the XML-reply to
client manipulating the master job. Also, a list of rendering devices is
added to the add-job pipeline, and is passed to the job as an
environment variable. What is missing is for IPCGLJobController to make
use of this environment variable.