tests: don't source envvar-check manually, test-lib.sh does it
tests: ensure at least one failure when $built_programs is empty
tests: improve perl-based tempdir handling
tests: reorder some tests in the long list
tests: put root-only (usually skipped) tests at the end
tests: move another file (expensive) into test-lib.sh
tests: cp/perm (usually not run) was failing on systems with SELinux
tests: do define built_programs
tests: update commented-out examples in sample-test, too
tests: don't fail in a non-English locale