Reduce memory footprint of the svnrdump dump handling by creating subpools
per file and directory instead of only per revision. Somehow everything was
prepared, but not finished here.

* subversion/svnrdump/dump_editor.c
  (make_dir_baton,
   make_file_baton): Make file/dir pool within parent.
  (delete_entry): Use parent pool for data in parent.
  (add_directory,
   open_directory): Don't use editor pool as scratch pool.
  (close_directory): Destroy directory pool.

  (add_file,
   open_file,
   apply_textdelta): Don't use editor pool as scratch pool.
  (close_file): Destroy file pool.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1557736 13f79535-47bb-0310-9956-ffa450edef68