Skip parallel/cobegin/test_big_recursive_cobegin on cygwin.

It has been timing out, but timedexec is not able to kill it.
Merge pull request #280 from thomasvandoren/skip-another-cygwin-test-that-does-not-timeout

Skip parallel/cobegin/test_big_recursive_cobegin on cygwin.

It has been timing out on cygwin testing, but timedexec is not able to kill it.

Similar behavior to test skipped in #175.