Following up on r1562043, make the data available handler for apr files
handle TIMEUP of the poll request as 'no data available'. Otherwise it
will return this value as an SVN_ERR_STREAM_NOT_SUPPORTED, which is
certainly not expected by ra_svn.

* subversion/libsvn_subr/stream.c
  (data_available_handler_apr): Handle timeout. Wrap error.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1581792 13f79535-47bb-0310-9956-ffa450edef68