Always include the test/ directory in tarfiles

Always include the test/ directory in tarfiles

In hindsight, it's hard to see why not including it was ever an option.
* make-dist: Always include the test/ directory.
(with_tests): Remove.
(--tests, --no-tests): Make these options no-ops.
* Makefile.in (mostlyclean_dirs, maintainer_clean_dirs): Add "test".
(mostlyclean, clean, distclean, maintainer-clean):
Remove special-casing for "test".
($(CHECK_TARGETS)): Simplify.