test for bug 891254

--HG--
extra : transplant_source : %FE%D3%7F%0F%3Da%3A%D9u6Hx2%E22%15fn%14H
remove unintentional ! in ed23ecc80370 to test expected buffer frame count when length is supplied b=890528

--HG--
extra : transplant_source : %BB%8E%A8%C2BBFr%A4D%28VG%84%2A%AE%A3qZ%81
use existing named constants b=890528

--HG--
extra : transplant_source : %C9%F5%23%A2%CC%D0%E5v%F4%7B%ED%93%0C%B6%D7%E3%CC%C5%B1%A1
Bug 909005: use getdents() on OpenBSD now that it is available r=glandium