Handle params key encoding error.

[nanaya]

Explicitly raise error in case of encoding error.

Updated to default decode to binary. Fixes(?) #610.

[nanaya]

Updated to encode string to binary by default.

[nanaya]

The alternative is to pass through whatever encoding the query string is using, something like this

def unescape(s)
  URI.decode_www_form_component(s, s.encoding)
end

[tenderlove]

Fixed by #713