merge this fix from trunk:

  Prevent hangs of child processes when writing to piped loggers at
  the time of graceful restart.  

PR:           26467
Reviewed by:  jorton, pquerna


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.0.x@202161 13f79535-47bb-0310-9956-ffa450edef68