Fix detection of O_NONBLOCK inheritance.

The original test failed occasionally on a busy
FreeBSD server when accept() returned EAGAIN.

Backport of r1449568 from trunk resp. r1449569
from 1.5.x resp. r1449570 from 1.4.x.


git-svn-id: https://svn.apache.org/repos/asf/apr/apr/branches/1.3.x@1449571 13f79535-47bb-0310-9956-ffa450edef68