Fix for "Clear call log" menu item showing up incorrectly.

The fragment member variables were being lost on rotation
because the FragmentManager does not call getItem on rotation.

Fix the way we save the fragments into member variables to ensure
that those references are always up to date so that mAllCallsFragment
is not null after rotation.

Bug: 17478780
Change-Id: I16b52711b336e8fd2d03453c5f20b9457b82694a