No match between user and token detailed pam values

This slight modification allows the pam module to distinguished two cases that may occur during the matching user-token phase : The user is not mentionned in the file (returns a user_unkown that may be useful for debugging configurations), the key does not match the user (in which case a auth_err is issued). Otherwise, the old authinfo_unavail is sent, as it used to be the case.

Indeed, before, all those were merged into the authinfo_unavail, which could be a problem because this value can have special meaning if you implemented a fallback for the validation server (in which case the module also uses authinfo_unavail)