Merged /httpd/httpd/trunk:r1811649,1811664,1814118

  *) ab: Make the TLS layer aware that the underlying socket is nonblocking,
     and use/handle POLLOUT where needed to avoid busy IOs and recover write
     errors when appropriate.  [Yann Ylavic]

  *) ab: Keep reading nonblocking to exhaust TCP or SSL buffers when previous
     read was incomplete (the SSL case can cause the next poll() to timeout
     since data are buffered already).  PR 61301 [Luca Toscano, Yann Ylavic]




git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x@1814468 13f79535-47bb-0310-9956-ffa450edef68