`drush @sites some-command` flaw when cancelling operation

drush_remote_command() takes care of running a command across multiple sites when it detects @sites (or --site-list). The function returns false if the user reject to perform the command. It should return true for drush's main loop to prevent trying bootstrap to a site.

jonhattan@jengibre:/var/www/drupal-6.x$ drush @sites up
You are about to execute 'up' non-interactively (--yes forced) on all of the following targets:
  #d620
  #d7sudb
  #d6
  #d620.com
  #adepsi
Continue?  (y/n): n
Aborting.                                                                                                          [cancel]
You are about to execute 'up' non-interactively (--yes forced) on all of the following targets:
  #d620
  #d7sudb
  #d6
  #d620.com
  #adepsi
Continue?  (y/n): n
Aborting.                                                                                                          [cancel]
Command pm-update needs a higher bootstrap level to run - you will need invoke drush from a more functional Drupal [error]
environment to run this command.
Command pm-update needs the following modules installed/enabled to run: update.                                    [error]
The drush command 'up' could not be executed.                                                                      [error]
Could not find a Drupal settings.php file at ./sites/default/settings.php.                                         [error]

I think proposed solution doesn't break anything.