Log Message:
vala: update to 0.38.8.

Vala 0.38.8
===========
 * Various bug fixes:
  - Fix GDestroyNotify of delegate parameters in delegate declaration [#639059]
  - Avoid critical when connecting dynamic signals
  - compiler: Prefix headers for set_cheader_override() if includedir is given
    [#793299]
  - Don't warn about unused internal methods which are meant to be visible
    on DBus [#593902]
  - libvaladoc: Prevent WITH_CGRAPH conditional having an impact on generated
    sources

 * Bindings:
  - gio-2.0: Cherry-pick some DBusProxy fixes from 0.40
  - gstreamer-1.0: Update from 1.13+ git master
  - gdk-3.0,gtk+-3.0: Update to 3.22.27