Added some tricky code to clear dirty bits in @auto trees after the write-at-file-nodes command.
An important Aha: the new code writes the .leo file (thereby writing changed persistence data), but *only* if there are no *other* changed nodes outside the persistence tree.
Otherwise, neither the persistence data nor the still-unwritten dirty nodes are written, and the .leo file remains dirty.
This could be called a compromise, but it is much better than several other alternatives I tried today.