message: Add explicit conversions to fix build on GCC 4.8
diff: @@ -189,11 +189,11 @@ public:
  iterator_bool_pair emplace(K&& key, T&& value) {
  auto i = lower_bound(key);
  if (i == end())
  - return xs_.emplace(copy(std::forward<K>(key)), std::forward<T>(value));
  + return xs_.emplace(copy(std::forward<K>(key)), V{std::forward<T>(value)});
  if (i->first == key)
  return {i, false};
  return {xs_.emplace_hint(i, copy(std::forward<K>(key)),
  - std::forward<T>(value)),
  + V{std::forward<T>(value)}),
  true};
  }
  @@ -207,18 +207,18 @@ public:
  template <class T>
  iterator_bool_pair insert(string_view key, T&& value) {
  - return emplace(key, std::forward<T>(value));
  + return emplace(key, V{std::forward<T>(value)});
  }
  template <class K, class T>
  iterator emplace_hint(iterator hint, K&& key, T&& value) {
  if (hint == end() || hint->first > key)
  - return xs_.emplace(copy(std::forward<K>(key)), std::forward<T>(value))
  + return xs_.emplace(copy(std::forward<K>(key)), V{std::forward<T>(value)})
  .first;
  if (hint->first == key)
  return hint;
  return xs_.emplace_hint(hint, copy(std::forward<K>(key)),
  - std::forward<T>(value));
  + V{std::forward<T>(value)});
  }
  template <class T>
  @@ -230,12 +230,12 @@ public:
  iterator_bool_pair insert_or_assign(string_view key, T&& value) {
  auto i = lower_bound(key);
  if (i == end())
  - return xs_.emplace(copy(key), std::forward<T>(value));
  + return xs_.emplace(copy(key), V{std::forward<T>(value)});
  if (i->first == key) {
  - i->second = std::forward<T>(value);
  + i->second = V{std::forward<T>(value)};
  return {i, false};
  }
  - return {xs_.emplace_hint(i, copy(key), std::forward<T>(value)), true};
  + return {xs_.emplace_hint(i, copy(key), V{std::forward<T>(value)}), true};
  }
  template <class T>
  @@ -247,7 +247,7 @@ public:
  hint->second = std::forward<T>(value);
  return hint;
  }
  - return xs_.emplace_hint(hint, copy(key), std::forward<T>(value));
  + return xs_.emplace_hint(hint, copy(key), V{std::forward<T>(value)});
  }
  // -- lookup -----------------------------------------------------------------
  