Revision 1719089

Continue debugging: try avoiding apr_hash_overlay() as it appears to be
returning a hash with duplicate keys in it (which should be impossible),
on the Mac buildbots. A follow-up to r1719056.

* subversion/libsvn_delta/branch_compat.c
  (hash_overlay): New.
  (drive_changes_r): Use hash_overlay() instead of apr_hash_overlay().