[vala] (6 commits) Non-fast-forward update to branch wip/issue/278

[Rico Tzschichholz <ricotz src gnome org>]

The branch 'wip/issue/278' 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:

  5dc573f... Add supported for sealed classes
  7c0d0ed... WIP

Commits added to the branch:

  5966203... glib-2.0: Bind strcmp0 as GLib.CompareFunc<string?> (*)
  8f86bb7... xtst: Fix signature of XTest.fake_relative_motion_event() (*)
  b35b0b1... vala: Add Symbol.is_extern and use/set is accordingly (*)
  70c4b16... codegen: Don't write declaration of extern symbols with giv (*)
  daaf264... Add supported for sealed classes
  ab20f50... WIP

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