queue_mail_key config item limited to 128 characters; should be longer, or a textarea for easier editing

Related to issue #965150: mailkey exclusion does not work at all.

Needs to be larger, in order to allow logintoboggan mailkeys. I suggest a minimum #maxlength of 512, or, ideally, it should be a multi-line text area.

I assume that newlines in the data (if we use a textarea) won't cause problems since we're splitting the config variable using preg_split in queue_mail.inc: $ignore_list = preg_split("/[\s,'\.\"]+/", variable_get('queue_mail_keys', ''));