Fix segfault in FSFS commit caused by a pool usage bug in verify_moves.

* subversion/libsvn_fs_fs/transaction.c
  (check_for_duplicate_move_source): allocate hash content in separate pool
  (verify_moves): don't use the iter_pool for common hash content

git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1525484 13f79535-47bb-0310-9956-ffa450edef68