Add new flag -T

[akirpa]

Perform 'make test' after build package

[stesser]

Sorry for the late reply - I have been the maintainer of the FreeBSD port for a long time, but did not have access to this Github repository.
Anyway, the pull request is incomplete, since it does not take the TEST_DEPENDS into account.
There is partial/incomplete support for the fetching of test dependencies, and they would need to be added to the build dependencies if the -T option has been given. (Normally, test dependencies should be built just before the tests are performed, not before the build starts, since the test dependencies might in some way depend on the port that is to be tested being available - this would require significant further changes to get right.)
I might add the required code to include these test dependencies, but I'm not convinced that adding them to the build dependencies does not lead to build errors or dependency loops for some ports ...