Merge r1481010 from trunk:

 * r1481010
   Fix issue 4365, multi-threaded svnserve pool memory use after clear.
   Justification:
     SEGV, particularly on Windows.
   Votes:
     +1: philip, danielsh, ivan



git-svn-id: https://svn.apache.org/repos/asf/subversion/branches/1.8.x@1482133 13f79535-47bb-0310-9956-ffa450edef68