Opening 1.7.x backport branch for r1564215.

git-svn-id: https://svn.apache.org/repos/asf/subversion/branches/1.7.x-r1564215@1564280 13f79535-47bb-0310-9956-ffa450edef68
On the 1.7.x-r1564215 branch: Merge r1564215 from trunk and
resolve the text conflicts.

git-svn-id: https://svn.apache.org/repos/asf/subversion/branches/1.7.x-r1564215@1564362 13f79535-47bb-0310-9956-ffa450edef68
Merge the 1.7.x-r1564215 branch:

 * r1564215
   Reduce dynamic memory usage during c/o and export.
   Branch: ^/subversion/branches/1.7.x-r1564215
   Justification:
     Without this patch, operations using the standard reporter (at least
     svn: c/o and export; probably same for httpv1) use more or less
     unbounded amounts of memory.  Dynamic peaks of up to 20GB have been
     observed.  With this patch, those peaks come down to 100MB which
     matches our claim to streaminess.
   Votes:
     +1: stefan2, philip, breser


git-svn-id: https://svn.apache.org/repos/asf/subversion/branches/1.7.x@1564619 13f79535-47bb-0310-9956-ffa450edef68