[vala] (8 commits) Non-fast-forward update to branch wip/gtkgir

[Rico Tzschichholz <ricotz src gnome org>]

The branch 'wip/gtkgir' 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:

  68f86a5... gtk+-3.0: Switch to GIR

Commits added to the branch:

  84c8584... vala: Don't transform an explicit "null" into a valid forma (*)
  3fe3f8b... Use type-check to determine a GenericType (*)
  61503f9... tests: Add further "use of generics in constructor" test (*)
  55be33e... vala: Convert last non-type-check-based usages of GenericTy (*)
  ff5a94f... Move type_parameter property to GenericType (*)
  ac0dbad... codegen: Don't create null-safe destroy-wrapper for Generic (*)
  1775fa5... girparser: Handle metadata for fields inside a transparent  (*)
  46cfcd3... gtk+-3.0: Switch to GIR (*)

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