Document current assumptions in FSFS.
Document current assumptions in FSFS.

* subversion/libsvn_fs_fs/fs_fs.c
  (pack_body):
    Add a docstring with a warning against subtle bugs that might be
    introduced by well-meaning new calls to this function.

git-svn-id: f8a4e5e023278da1e04e203c7fe051e3c4285d88@1043595 13f79535-47bb-0310-9956-ffa450edef68

wbond/subversion,wbond/subversion,wbond/subversion,wbond/subversion,wbond/subversion,YueLinHo/Subversion,YueLinHo/Subversion,YueLinHo/Subversion,YueLinHo/Subversion,wbond/subversion,YueLinHo/Subversion,YueLinHo/Subversion,YueLinHo/Subversion,wbond/subversion,YueLinHo/Subversion