[vala] (4 commits) Non-fast-forward update to branch wip/issue/879

[Rico Tzschichholz <ricotz src gnome org>]

The branch 'wip/issue/879' 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:

  7b86c5d... WIP codegen: Improve *_get_type() fast path (glib >= 2.58)

Commits added to the branch:

  8677f09... vala: Improve error message for unsupported inner types and (*)
  8ee44db... vala: Don't allow "va_list" as return-type or type of field (*)
  7551bbb... codegen: Remove unreachable code in TypeRegisterFunction.in (*)
  6b03920... codegen: Improve *_get_type() fast path (requires glib >= 2 (*)

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