[vala] (5 commits) Non-fast-forward update to branch staging

[Rico Tzschichholz <ricotz src gnome org>]

The branch 'staging' 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:

  dca6f6a... codegen: Actually free data when using "remove(_all)" on GL

Commits added to the branch:

  b88fa50... vala: No need to run return_type.check() twice for method
  1be3531... vala: More thorough check of ValueType and set CodeNode.err
  7fbc73b... tests/girwriter: Add missing type-argument
  2094ff6... tests: Add more "type-arguments" tests to increase coverage
  d3e5013... vala: Stricter check of type-arguments for non-external met