pkglint(1) determines its list of basic variable types by grepping
itself for certain if/elsif conditions. This combination of cleverness
and large conditional block should be replaced with simple,
table-driven code. But first we have to get the functionality under
test, which I've begun to do here.

Initialize a package global with the contents of $0, and override
it in test (otherwise self-grepping breaks because $0 is the test
script). Extract the dirty Test::Trap details to test_unit(). Test
main() for a few common values of @ARGV. Notice the aforementioned
cleverness because it broke an expected success, and fix it just
enough to test get_vartypes_basictypes() for a couple expected
types.

No functional change intended. I've manually tested the small changes
to pkglint.pl and have also verified that a couple packages lint
the same as before.

(schmonz)