• Disallow duplicate keys by default, only allow them in relaxed
  mode. (#75)
  Analog to invalid unicode, which does error by default.
  RFC 7159 section 4 says that "The names within an object should be unique."
  So it's either i_ (undefined) or n_ (errors).
  See http://seriot.ch/parsing_json.php#24
  This is different to the other JSON modules, which do have a different
  interpretation of the spec. Use relaxed for backcompat if you want to
  allow duplicate keys.
  
• De-fragilize t/96_mojo.t false test to "". It mostly is.