Multiple locations in the code use $m->request_args to obtain
information about the query parameters that were specified in the URL;
however, the values recovered from this call are not utf8-decoded, which
can lead to corrupted data.  Additionally, existing code may depend on
$m->request_args being encoded, which prevents merely altering the data
prior to its entry into Mason.

Provide a global variable, $DECODED_ARGS, which provides the correct,
decoded, query parameters.