Perl version strings are flawed in a few ways. Convert them to
user-friendly strings when printed so that Git tags and tarball names
are easier for downstream distributions to work with.
Now all that is needed to add a new unit test is to create a `t/*.pl`
file and list it in the `handwritten_tests` variable.
To run the test suite, run:
./autogen && ./configure && make check
Fixes#147
