make check seems to be more common than make test, and "check" is the
recommended name according to the GNU standards. This patch teaches
the build system to support both targets. It also marks the test-clean,
check and test targets as phony.
tests := $(sort $(wildcard $(test_dir)/t[0-9][0-9][0-9][0-9]-*.sh))
+check: $(tests)
test: $(tests)
$(tests): all
$(RM) -r $(results_dir)
$(RM) -r $(trash_dir)
-.PHONY: $(tests) test-help
+.PHONY: $(tests) test-help test-clean test check