In FSFS, use sub-pools for temporaries in those API function implementations
that call open_path().

All these functions are complex enough to make the overhead of creating a
temporary sub-pool be outweighed by the benefits of tighter memory usage and
better isolation from pool usage scheme.

* subversion/libsvn_fs_fs/tree.c
  (fs_change_node_prop,
   fs_make_dir,
   fs_delete_node,
   fs_make_file): These functions don't return allocated memory, so use
                  the new sub-pool for all allocations.
  (apply_textdelta): Allocate the node to be stored in the baton in the
                     baton's pool.  That way, all remaining allocations
                     from POOL are temporaries.
  (fs_apply_textdelta): Pass a temporary sub-pool to the above function.
  (apply_text,
   fs_apply_text): Same as for apply_textdelta and fs_apply_textdelta.
  (fs_closest_copy): Use a temporary sub-pool for all queries that don't
                     produce the objects to return.

git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1648253 13f79535-47bb-0310-9956-ffa450edef68