[vala] (8 commits) ...vala: Allow explicit interface methods to be virtual

[Rico Tzschichholz <ricotz src gnome org>]

Summary of changes:

  83112b2... vala: Add GenericType.get_actual_type() (*)
  25f8caf... vala: Allow get_actual_type() to be used for expected failu (*)
  3399a1c... vala: Add Method.compatible_no_error() (*)
  8bc6cc7... vala: Don't just guess and check for a matching base_interf (*)
  7c8f91b... vala: No need to look further if an implementations was fou (*)
  3da2f97... vala: Search in all interfaces for an implementation match  (*)
  7dcf561... codegen: Use properly checked implicit interface implementa (*)
  2cea36a... vala: Allow explicit interface methods to be virtual (*)

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