Provide 2.x upgrade guidance for services

Half the problem was #1987026: drushrc.php no longer read from Drupal root in Drush 5 which, in the case of provision_civicrm, meant we weren't ever having our code triggered. With that solved, the changes required to support class auto-loading became clearer. I've documented them here: http://community.aegirproject.org/upgrading/path#Class_auto-loading. This needs a technical review, as it's still pretty new to me. In addition, I'm not sure it's appropriate for that page, which is focused more on providing guidance to administrators upgrading their Aegir install, rather than developers porting their extensions. Perhaps a sub-page is in order, or perhaps a new page in the Developer's Guide (which itself should probably be revised and updated).

Half the problem was #1987026: drushrc.php no longer read from Drupal root in Drush 5 which, in the case of provision_civicrm, meant we weren't ever having our code triggered. With that solved, the changes required to support class auto-loading became clearer. I've documented them here: http://community.aegirproject.org/upgrading/path#Class_auto-loading. This needs a technical review, as it's still pretty new to me. In addition, I'm not sure it's appropriate for that page, which is focused more on providing guidance to administrators upgrading their Aegir install, rather than developers porting their extensions. Perhaps a sub-page is in order, or perhaps a new page in the Developer's Guide (which itself should probably be revised and updated).

I'm continuing to work through this with hosting_/provision_civicrm, and it appears that what I've documented so far isn't sufficient. While it'll write values from the front-end into the site alias, it won't necessarily be available through d(). In particular, I'm seeing this in a drush_hook_post_provision_install(). I've had to add d()->init(); early in the hook implementation, and option_documentation() methods to the classes, like so:

static function option_documentation() {
  return array(
    '--civicrm_version' => 'Project: The codename for this project.',
  );
}

Both appear to be required, but I'm at a bit of a loss to explain it. I haven't implemented an init() method in my classes, so I guess it's using the parent's init(), which in the case of Provision_Service, doesn't appear to do anything: http://api.aegirproject.org/api/Provision/Provision--Service.php/functio....

Is it maybe triggering the __construct() method on the parent? I have to admit I don't really understand what's going on here.

With #7 and the inclusion of #2103173: Provide an example of saving data to a site context, I think we can close this issue.