lang/smalltalk: try to unbreak the port's build on fresh -CURRENT

While here, define LICENSE (GPLv2+) and hook the test suite to our
framework. Currently, out of 130 tests, 8 fail (7, 8, 32, 41, 70,
118, and 122 with 1 expected failure), 1 test was skipped.

Reported by: pkg-fallout