t/test-meta.sh: handle systems that have sgid directories.

Explicitly chown the test directory to a group we're in so that the
tests will work on systems that have sgid directories by default
(i.e. NetBSD, etc.).

Thanks to Thomas Klausner <tk@giga.or.at> for reporting the problem
and helping track down the solution.

Signed-off-by: Rob Browning <rlb@defaultvalue.org>
id-other-than: exclude names based on their underlying ids.

This fixes a failure on systems that have more than one one user/group
name mapped to the same id (i.e. NetBSD's root/toor accounts).

Thanks to Thomas Klausner <tk@giga.or.at> for reporting the problem
and helping track down the solution.

Signed-off-by: Rob Browning <rlb@defaultvalue.org>