Currently addport -a ends up running a command line like:
make PORTSDIR="/tmp/ap.BsOuZJBy" clean check-categories
where the temporary directory has only parts of the ports tree
(specifically bits under ${PORTSDIR}/Mk) checked out. This can't work
as 'make check-categories' needs to see the entire ports tree checked
out.
Instead, run the checks specified by '-a' and '-t' with the value of
$PORTSDIR from the environment.