Merge the r1579684 group from trunk:

 * r1579684, r1580867, r1580872
   Fix issue #4481 "automatic merge confused by missing subtree merge".
   Justification:
     Valid merges were broken (and gave a confusing error message).
   Votes:
     +1: julianfoad, rhuijben, philip


git-svn-id: https://svn.apache.org/repos/asf/subversion/branches/1.8.x@1586555 13f79535-47bb-0310-9956-ffa450edef68
Merge r1583580 from trunk:

 * r1583580
   Skip a test that fails when run as root.
   Justification:
     Avoids spurious FAIL.
   Votes:
     +1: philip, rhuijben, julianfoad


git-svn-id: https://svn.apache.org/repos/asf/subversion/branches/1.8.x@1586556 13f79535-47bb-0310-9956-ffa450edef68
Merge r1586255 from trunk:

 * r1586255
   Fix propget/proplist error on invalid revisions
   Justification:
     Replaces easy to trigger assertions with proper errors.
   Votes:
     +1: rhuijben, julianfoad, philip


git-svn-id: https://svn.apache.org/repos/asf/subversion/branches/1.8.x@1586557 13f79535-47bb-0310-9956-ffa450edef68
Merge r1481782 from trunk:

 * r1481782
   Fix problem in test suite by allocating buffer of the right size
   Justification:
     Reported to fail often when tracing memory problems.
   Votes:
     +1: rhuijben, stsp, philip


git-svn-id: https://svn.apache.org/repos/asf/subversion/branches/1.8.x@1586558 13f79535-47bb-0310-9956-ffa450edef68