Fix a major latency snafu in svnserve.  Sequences of small requests
and responses would be delayed in the TCP/IP stack by Nagle's alogrithm.
That becomes obvious when e.g. running "ls -R".

* subversion/libsvn_ra_svn/marshal.c
  (svn_ra_svn_create_conn3): send data as soon as write copy it from
                             our send buffers to the socket

git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1533530 13f79535-47bb-0310-9956-ffa450edef68