Merge branch 'ib/test-selectively-run'

Allow specifying only certain individual test pieces to be run using a range notation (e.g. "t1234-test.sh --run='1-4 6 8 9-'"). * ib/test-selectively-run: t0000-*.sh: fix the GIT_SKIP_TESTS sub-tests test-lib: '--run' to run only specific tests test-lib: tests skipped by GIT_SKIP_TESTS say so test-lib: document short options in t/README