Currently, if you meld directories which have 100 identical subdirectories
and 1 different file, the 100 identical subdirectories are unconditionally
displayed.  It would be great if identical subdirectories could be turned
off in the view (i.e., only different files and their ancestors are display).

I looked at the code, and the control flow makes this a little difficult to
implement, since there's currently no place in the code where a directory is
explicitly known to have not changed.  Is there a way to have an invisible
entry in the treeview (i.e., could directories be added invisible and then
appear only if they're expanded)?

Thanks!