remove zfs from the exception list; it now works like the other fs's.

update copyright.

skip userlevel filesystems that have their own rules (they depend on the
system setting of the sysctl on NetBSD) and zfs because it implements its
own rules for hardlinks to files (does its own permission checks).

ignore EOPNOTSUPP errors for fs's that don't support hard links.

Add a test for hardlink sysctl limiting.

update copyright.

skip userlevel filesystems that have their own rules (they depend on the
system setting of the sysctl on NetBSD) and zfs because it implements its
own rules for hardlinks to files (does its own permission checks).

ignore EOPNOTSUPP errors for fs's that don't support hard links.

Add a test for hardlink sysctl limiting.