tests defs: more namespace-safeness ($using_tap): Renamed ... ($am_using_tap): ... to this. ($parallel_tests): Renamed ... ($am_parallel_tests): ... to this. ($test_prefer_config_shell): Renamed ... ($am_test_prefer_config_shell): ... to this. ($original_AUTOMAKE): Renamed ... ($am_original_AUTOMAKE): ... to this. ($original_ACLOCAL): Renamed ... ($am_original_ACLOCAL): ... to this. * tests/defs, tests/defs-static.in, tests/gen-testsuite-part, tests/README, and all callers: Adjusted. * tests/Makefile.am (AM_TESTS_ENVIRONMENT): Adjust, and rewrite to make future adjustments easier. * tests/defs (funcs_file_): Renamed ... (am_funcs_file): ... to this. * Makefile.am (sc_tests_obsolete_variables): New maintainer check. (syntax_check_rules): Add it.