Comment 2 for bug 251858

I decided that the client shouldn't directly know about things like pref keys and drivers.

For SUEnableAutomaticChecksKey, SUUpdater is KVC/KVO-compliant for automaticallyChecksForUpdates.

For SUFeedURLKey, SUUpdater is KVC/KVO-compliant for feedURL.

For [[[NSApp delegate] sparkleUpdater] checkForUpdatesWithDriver:[[[SUScheduledUpdateDriver alloc] init] autorelease]], use SUUpdater's -checkForUpdatesInBackground.