Merge r1563110 from trunk:

 * r1563110
   Correct the default cache size in svnserve's help text for the -M option.
   Justification:
     Help text is wrong.
   Votes:
     +1: philip, stefan2, breser


git-svn-id: https://svn.apache.org/repos/asf/subversion/branches/1.8.x@1565073 13f79535-47bb-0310-9956-ffa450edef68