[mutter] (13 commits) Non-fast-forward update to branch wip/carlosg/xwayland-startup-side-channel

[Carlos Garnacho <carlosg src gnome org>]

The branch 'wip/carlosg/xwayland-startup-side-channel' was changed in a way that was not a fast-forward 
update.
NOTE: This may cause problems for people pulling from the branch. For more information,
please see:

 https://wiki.gnome.org/Git/Help/NonFastForward

Commits removed from the branch:

  1ca2e99... core: Use DISPLAY envvar to forward in the launch context
  ce0171f... wayland: Set up initialization X11 socket
  2f9338b... wayland: Pass private X connection on GNOME_SETUP_DISPLAY
  6560130... xwayland: Allow setting up maintenance processes

Commits added to the branch:

  d30ef0d... cogl/clip-stack: Use "merge" parameter for rectangle clips (*)
  7205433... cogl/clip-stack: Restore old matrices after drawing to sten (*)
  1e0b015... cogl/clip-stack: Explicitely initialize the stencil mask (*)
  46e38ff... cogl/clip-stack: Set color and depth mask when drawing rect (*)
  0ada900... wayland/actor-surface: Check for MetaXwaylandSurface instea (*)
  372d73e... surface-actor: Cull out surfaces without alpha channel (*)
  6831f2e... window-actor/x11: Disable culling on window actor level (*)
  c979cd9... surface-actor: Do not copy empty clip/unobscured regions (*)
  39a8c04... background-actor: Do not copy empty clip/unobscured regions (*)
  38e58b8... core: Use DISPLAY envvar to forward in the launch context
  166a464... wayland: Set up initialization X11 socket
  e3149e6... wayland: Pass private X connection on GNOME_SETUP_DISPLAY
  64eaf70... xwayland: Allow setting up maintenance processes

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