LP#1568046: Replace last two uses of connectby with other function calls.

LP#1568046: Replace last two uses of connectby with other function calls.

Modify permission functions permission.usr_has_perm_at_nd and
permission.usr_has_perm_at_all_nd to no longer require the connectby
function from the tablefunc extension.  The connectby functionality is
replaced by existing database functions to retrieve org. unit
descendants.

This change removes the need to load the tablefunc extension, so it is
dropped from the create scripts.  The upgrade script does not remove
the extension as sites may be using connectby or other functions from
the extension.

Signed-off-by: Jason Stephenson <jason@sigio.com>
Signed-off-by: Ben Shum <ben@evergreener.net>