Update drupal.org docs to reflect recent drush core/contrib shell updates capabilities

Waiting on #434944: Allow minor upgrades of drupal core.

#1 was a bit of a red herring, as the issue in question is about minor upgrades, whereas the documentation page in question relates to a major upgrade from Drupal 5 to Drupal 6. Drupal 5 is not even supported by Drush-5, so this is at best a Drush-4 issue. However, the site-upgrade command in Drush-4 will only upgrade from Drupal 6 to Drupal 7, and it even has some issues doing that. See #1410344: Remove site-upgrade command from Drush-4.x.. The contrib Drush site upgrade project could in theory be made to support Drupal 5 to Drupal 6 upgrades (if Drush does not fail calling pm-* functions on the D5 site), but it would require a co-maintainer to come in and implement that.

If sup is removed from Drush-4, perhaps we could move this to "postponed" in the drush_sup queue, pending D5 support in that project.

This issue was marked closed (won't fix) because Drush has moved to Github.

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