Bug 932898 - Fix leaks in /browser/base/content/test/general/ r=jaws

From 703bffabe0374690ecce1ca6a82cfb1f1ace30e8 Mon Sep 17 00:00:00 2001
Bug 930970 - migrate based on pref, r=Unfocused,jaws
Bug 930970 - Fix bustage caused by tests assuming this._rdf is created within migrateUI, rs=bustage