Update PackageMonitor to recognize new 'replacing' semantics

The ACTION_EXTERNAL_APPLICATIONS_UNAVAILABLE broadcast now uses the
EXTRA_REPLACING intent extra when it is sent as part of an upgrade operation
on a forward-locked application.  Update PackageMonitor to recognize this
new information and express it appropriately to the observer.

Bug 11988313

Change-Id: I34dfaa965dd322f4fa8945e7b83c9f2e8cf5269a