Avoid unnecessary use of Exporter
Rework unit tests for NetBSD, OpenBSD

Case 117021: Rework unit tests to address failures as identified by the CPAN
test server infrastructure, due to NetBSD and OpenBSD tar's lack of support
for GNU LongLink extensions

Specific changes:

    * Detect BSD tar and skip certain tests as deemed reasonable

    * Adjust tests to strip trailing and leading slashes from pathnames
      when testing expected and provided outputs