Not only this shrinks the size of the generated Makefile (from > 6300
lines to ~3000), but will allow further simplifications in future
changes.
* tests/Makefile.am (TEST_EXTENSIONS): Add '.sh' and '.pl'.
(PL_LOG_COMPILER, SH_LOG_COMPILER): New, still defined simply to
$(LOG_COMPILER) for the time being.
(TESTS, root_tests): Adjust as described.
* All tests: Rename as described.