Fix a pool usage issue with tree deletion.  Not sure whether it gets
actually triggered by "normal" use.  Patch FSFS and FSX; BDB uses
different code.

* subversion/libsvn_fs_fs/dag.c
  (svn_fs_fs__dag_delete_if_mutable): Add a missing iterpool to the
                                      recursive loop.

* subversion/libsvn_fs_x/dag.c
  (svn_fs_x__dag_delete_if_mutable): Do the same for FSX.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1647820 13f79535-47bb-0310-9956-ffa450edef68