The unit-test execution has been refactored to run inside a regular
'test-lib.sh' shell script, which allows unit tests to benefit from
standard test setup like sanitizer options and logging. The test
suite's interaction with external TAP generators and JUnit XML
reporting has also been cleaned up and simplified.
* jk/unit-tests-via-test-lib:
test-lib: drop the shell JUnit XML reporting code
test-tool: drop the run-command testsuite mode
t: drop redundant unit-test invocations
t: run clar unit tests through test-lib.sh
test-lib: allow an external program to supply TAP output
test-lib: stop inventing a JUnit testcase for empty suites
test-lib: drop unused test_external_has_tap variable
unit-tests: report the correct unexpected argument