Prevent creating iRODSUser of type rodsgroup

[alanking]

Even though groups are just users without passwords in iRODS, it seems to me that it would be nice to keep the iRODSGroup and iRODSUser types separated completely by not allowing iRODSUsers of type rodsgroup or iRODSGroups of any type other than rodsgroup.

[d-w-moore]

And presumably, to go along with that, some future version of iRODS will also make a stronger distinction between users and groups, with such queries as this one returning zero rows.

$  iquest "select USER_ID where USER_NAME = 'public'"
USER_ID = 10001