Advice in previous commit did not actually work; change recommendation to 'drush dl srush_sup-7.x-2.x --select'

#1809116 by greg.1.anderson and benjifisher: Give more specific instructions on downloading drush_sup in README.txt

Rename to upgrade.drush.inc so that it will be easier to use drush dl to get latest code. Update README.txt to match.

Use 'integrate' mode instead of 'interactive' when calling updatedb, and save status messages printed during updatedb. Factor out stages and mappings to separate files.

Make status report run on the target site. Update README with latest status and wishlist features. Standardize on 'stage' instead of 'state' for FSM transistions.