[gdm] (5 commits) ...Merge branch 'benzea/wait-seat-graphical' into 'master'

[Ray Strode <halfline src gnome org>]

Summary of changes:

  de7df6f... daemon,common,libgdm: Drop use of sd_seat_can_multi_session (*)
  05febec... local-display-factory: Rename create_display to show it is  (*)
  d2a06b4... local-display-factory: Move session type checking into crea (*)
  a37e5a9... local-display-factory: Wait for seats to become graphical (*)
  e04376f... Merge branch 'benzea/wait-seat-graphical' into 'master'

(*) This commit already existed in another branch; no separate mail sent