Blind people do not connect screens

[Samuel Thibault]

Hello,

Some blind people report that Xorg refuses to start when no screen
is connected to their machine.  Of course they could configure their
xorg.conf to use the dummy driver, but then they'd have to modify it
back when using a screen etc. and distributions are more and more going
towards full autodetection anyway.  I don't know which way would be
fine:

- have drivers not fail when no screen is connected, but use some
  default sane resolution.  Needs cooperation from all drivers.
- have X.org fallback to dummy when no screen is connected.  If screen
  detection works correctly, shouldn't harm sighted users.  Needs
  information feedback from drivers to tell so.
- have X.org fallback to dummy when the autodetect driver does not work.
  May make sighted users wonder why their screen is black, but well.
- introduce an xorg.conf option to enable some behavior above.  Doesn't
  really match nowadays' "no xorg.conf" moto.
- introduce an option similar to -allowMouseOpenFail.  Not really
  convenient to automatically configure in a generic-purpose
  distribution.

Samuel