Reduce peak memory footprint for very large directories in FSFS.
Reduce peak memory footprint for very large directories in FSFS.

* subversion/libsvn_fs_fs/cached_data.c
  (svn_fs_fs__rep_contents_dir,
   svn_fs_fs__rep_contents_dir_entry): Don't serialize directories that
                                       won't fit into the cache.

git-svn-id: f8a4e5e023278da1e04e203c7fe051e3c4285d88@1725180 13f79535-47bb-0310-9956-ffa450edef68

YueLinHo/Subversion,YueLinHo/Subversion,YueLinHo/Subversion,YueLinHo/Subversion,YueLinHo/Subversion,YueLinHo/Subversion,YueLinHo/Subversion,YueLinHo/Subversion