[vala] (8 commits) ...vala: Allow assignment of 0U to enum types

[Rico Tzschichholz <ricotz src gnome org>]

Summary of changes:

  5c19009... gsignal: get_detail_cexpression/get_signal_name_cexpression (*)
  abbdfdd... tests: Extend "detailed signal" test to increase coverage (*)
  ed72aa2... gsignal: Use guint to represent flags-enum in custom GMarsh (*)
  a8d1c68... gsignal: Move disconnect error from signal-module to semant (*)
  371512e... tests: Extend "struct with delegate" test to increase cover (*)
  0d09b1d... tests: Add "method ccode return-type" test to increase cove (*)
  9199f6a... ccodegen: Use unsigned default value for flags-enum (*)
  2703619... vala: Allow assignment of 0U to enum types (*)

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