[vala] Non-fast-forward update to branch 0.52

[Rico Tzschichholz <ricotz src gnome org>]

The branch '0.52' 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:

  6469f80... codegen: Fix property access inside opaque compact class
  a5c4c47... glib-2.0: Current constants in GLib.Math are part of glib.h
  28bf571... tests: Extend "field access" tests to increase coverage
  3600607... glib-2.0: Add RefString since 2.58
  d1d4828... gio-2.0: Unhide a few usable symbols which are marked not i
  fd1811e... vala: Warn about unsupported cast to void and drop it
  e7079f3... valadoc: Correctly format background of inline @link's
  0d7d172... vala: Don't restrict element type of GLib.Array
  e2bb920... codegen: Add type declaration for implicit temporary local 

Commits added to the branch: