Autosave: now the best implementation ever?  (YES.)

The new Undo/Redo engine is proving itself useful in a lot of unexpected
ways.  Its latest awesome contribution?  PD's Autosave engine can now
reconstruct *an entire previous session*, including every open image AND
every image's full Undo/Redo stack.

This means that if the program goes down (from PC fails, power outage,
etc) in the middle of any edit action, the next time PD is run, it will
restore all open images to their exact state, in their exact position in
each Undo/Redo stack, and with all Undo/Redo entries still fully
functional.

This means the user will never be screwed by the Autosave engine
restoring an unwanted state, because the Autosave engine will create a
session where Undo works exactly as it did in the original session.

I've honestly never seen an implementation like this, so forgive me if
I'm overly giddy about how awesome this is.  :)