merge r1538171 from trunk:

APR_FOPEN_NONBLOCK is expected to be critical for an app
that uses it; return APR_ENOTIMPL instead of ignoring it if
not supported.


git-svn-id: https://svn.apache.org/repos/asf/apr/apr/branches/1.5.x@1538174 13f79535-47bb-0310-9956-ffa450edef68