VMS nits in cpan/Test-Harness/t/source.t

[Reapplying ada6eeb82df as it's still awaiting application
upstream two years later and the things it fixes get broken
again every time a new version of Test::Harness is brought
into blead.]

1.)  Can't get the basename of a directory in native format.

2.)  Symlinks still a bit dodgy -- skip tests for now.

Submitted upstream at:

https://rt.cpan.org/Ticket/Display.html?id=64353