message: vector: Always include pretty print instanciation.
diff: #include <ostream>
  #include_next <vector>
  -#include <elle/print-fwd.hh>
  +#include <elle/print/object.hh>
  namespace std
  {
  @@ -11,12 +11,12 @@ namespace std
  ostream&
  operator <<(ostream& out, vector<Args...> const& s)
  {
  - auto const format = is_fixed(out) ? "%s%f" : "%s%s";
  out << '[';
  auto* sep = "";
  for (auto const& e: s)
  {
  - elle::print(out, format, sep, e);
  + elle::_details::print(out, sep);
  + elle::_details::print(out, e);
  sep = ", ";
  }
  out << ']';
  