Merge branch 'rj/test-ulimit-on-windows'

On Cygwin, "ulimit -s" does not report failure but it does not work at all, which causes an unexpected success of some tests that expect failures under a limited stack situation. This has been fixed. * rj/test-ulimit-on-windows: t9010-*.sh: skip all tests if the PIPE prereq is missing test-lib: use more compact expression in PIPE prerequisite test-lib: don't use ulimit in test prerequisites on cygwin