tests: more use of TAP in our own testsuite * tests/parallel-tests-interrupt.test: Renamed ... * tests/parallel-tests-interrupt.tap: ... to this, and converted to the use of TAP protocol. * tests/self-check-cleanup.test: Renamed ... * tests/self-check-cleanup.tap: ... to this, and converted to the use of TAP protocol. * tests/self-check-dir.test: Renamed ... * tests/self-check-dir.tap: ... to this, and converted to the use of TAP protocol. * tests/self-check-is_newest.test: Renamed ... * tests/self-check-is_newest.tap: ... to this, and converted to the use of TAP protocol. * tests/self-check-unindent.test: Renamed ... * tests/self-check-unindent.tap: ... to this, and converted to the use of TAP protocol. * tests/list-of-tests.mk: Update.