Grab r175 from upstream. The patch doesn't apply cleanly, so I
manually applied and indented properly.

Suggested by: danielsh

* tools/server-side/svnpubsub/daemonize.py:
  (Daemon.daemonize): apply r175 concept. use O_EXCL.


git-svn-id: https://svn.apache.org/repos/asf/subversion/branches/1.8.x-r175-daemonize@1515871 13f79535-47bb-0310-9956-ffa450edef68