Merge the 1.9.x-r1860936 branch:

 * r1860936, r1860951, r1860958
   Provide a way for svnserve's 'get-deleted-rev' API to return 'not deleted'.
   Justification:
     Error handling was inconsistent across RA layers.
   Branch:
     ^/subversion/branches/1.9.x-r1860936
   Votes:
     +1: julianfoad, stsp


git-svn-id: https://svn.apache.org/repos/asf/subversion/branches/1.9.x@1863312 13f79535-47bb-0310-9956-ffa450edef68