The preference controller no longer permanently retains every object stored as a...

The preference controller no longer permanently retains every object stored as a preference... which means that classes using it have to be appropriately responsible.  The fast user switching support plugin was storing `NSNumber` objects used when fast user switching or the screensaver changes (when such activities are supposed to cause status changes) without retaining them. This fixes that and so fixes crashiness.

Fixes #9040. Fixes #9060.

git-svn-id: svn://svn.adiumx.com/adium/trunk@22496 1c916fce-81e2-0310-a464-8ca513f45935