Merge r1490684 from trunk:

 * r1490684
   Return 500 rather than 409 when commit fails and it is not a conflict.
   Justification:
     Not a client failure so 4xx is wrong.
   Votes:
     +1: philip, brane, breser


git-svn-id: https://svn.apache.org/repos/asf/subversion/branches/1.7.x@1514572 13f79535-47bb-0310-9956-ffa450edef68