[PATCH 0/6] libweston: Support multiple seats better

[nerdopolis]

I am resending as I messed up one of the commit messages, which resulted
in a very long subject by mistake. These patches fix issues with Weston
where it supports multiple seats better. 

Firstly supporting automatically detecting the seat to use, by using the
XDG_SEAT variable set by logind if the --seat option is not specified.

And then improving the fbdev-backend to support the --seat option and
not hard use seat0

And then to not have weston try to use a TTY when it's not running 
on seat0, as only seat0 can have TTYs

And also attempt to turn on a framebuffer device on, as many secondary
video cards that support DRM/KMS, such as qemu's bochs, and udl start 
off powered off, and don't turn on the screens until the ioctl is sent

Then finally, make the fbdev-backend detect the first framebuffer device
assigned to the current seat with udev (I based that largely off of some
of drm-backend)