Merge r1561040 from trunk:

Using UDS, we sometime try ops not supported on UDS. Make this
a known (and therfore handable) issue

Reviewed/backported by: jim


git-svn-id: https://svn.apache.org/repos/asf/apr/apr/branches/1.6.x@1590618 13f79535-47bb-0310-9956-ffa450edef68