Merge pull request #371 from ralfjung-e/develop

Fix bridge checking
Add support for passing -configdir to secondary X (GH-222)
Factor out PM and module (un)loading in bbsecondary.c
Remove unused status_secondary
start_secondary: bool arg: need_secondary, return: success
Add "none" accel/display bridge

The proper way to run nvidia settings is

    optirun -b none nvidia-settings -c :8
Add udev rules to create device files
Implement --no-xorg (GH-89)
Print more options when dumping configuration