Had a race condition in previous version.  Was supplying
internal_ft_delta list when applying changes and when undoing
changes.  From internal_ft_delta list, would construct apply and undo
sets.  However, if receive a backout message, then atomic objects in
internal_ft_delta list also get backed out and reset.  In these cases,
we cannot construct flow mods for undoing correctly.

Note: still may have a bug if backout before build FTableUpdate list.
Added FIXME describing it.