Fixes PopupPresenter

Yet another complication because we have no reliable tear down call from View
under Gingerbread. Cannot call dropView from  PopupPresenter#onSave because
that breaks resume. (Sample app masks this because its onResume behavior is
inefficient, creates new views all the time.) But if we don't tear it down the
PopupPresenter may still have a reference to, say, the portrait Popup when
its been rotated to Landscape. Result is double dialogs.

Fix is to make takeView() tear down the old dialog if there is one before
accepting the new view.