message: Allow users to omit "global." suffix
diff: @@ -457,8 +457,12 @@ optional<T> get_if(const std::map<std::string, config_value::dictionary>* xs,
  const std::string& name) {
  // Get the category.
  auto pos = name.find('.');
  - if (pos == std::string::npos)
  + if (pos == std::string::npos) {
  + auto i = xs->find("global");
  + if (i == xs->end())
  return none;
  + return get_if<T>(&i->second, name);
  + }
  auto i = xs->find(name.substr(0, pos));
  if (i == xs->end())
  return none;
  