Add --strict=0 to pm-releases command to work around a problem with the Drush command not documenting the --default-major option.

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.

Test for $update_free_status == false, and check if the destination site is already offline in steps 17 and 18, respectively. Also mark the "run cron" and "show status report" steps as "straightforward", so that they will run without prompting unless in --prompt-all mode.

#1703148 by greg.1.anderson: Implement --core-unmodified and --module-order options to allow pre-selection of these stages of the upgrade process via the cli

Allow --create-db to be passed along to sql-sync; insure that settings.php is rewritten in transitional site record

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

Use drush_invoke_process instead of drush_invoke to download Drupal. Fix up 'integrate' settings for all calls to drush_invoke_process.

Assume that a missing 'ok' state transition should go to the next sequential state in the fsm. Remove all trivial state transitions (most of them). Nice.

Fix some problems that crept in to the re-use code case; bring back some code accidentally removed in the last commit.