Add some documentation for the depth-based filter editor logic.
Add some documentation for the depth-based filter editor logic.

* subversion/libsvn_delta/depth_filter_editor.c
  (struct edit_baton, struct node_baton, okay_to_edit): Add docstrings
    and other commentary to help future readers comprehend this stuff.

git-svn-id: f8a4e5e023278da1e04e203c7fe051e3c4285d88@871636 13f79535-47bb-0310-9956-ffa450edef68

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