Comment 9 for bug 391965

One possible way: appcast.delegate.updater. I see two problems with this:

1. SUUpdateDriver doesn't include a getter for obtaining its updater (fixable).
2. This requires assuming that the appcast's delegate is non-nil and is an update driver.

The more I look at the code and think about this, the more I think that SUAppcast is not the proper place to perform this sort. I should do it in SUBasicUpdateDriver instead, so that I can sort by the custom comparator if there is one.