Set foreground priority for shutdown receivers.

The broadcast of ACTION_SHUTDOWN has a timeout of 10 seconds. To
reduce the risk of hitting the timeout and speeding up the
shutdown sequence in ShutdownThread we set the priority of the
BroadcastReceivers to FLAG_RECEIVER_FOREGROUND.

We have seen that this change reduces the shutdown time when
the system is under heavy load.

Change-Id: I22cbf6af8cf6fc4bdefaa1c3da8a7eed7e7b7674
Fix for third party installing with HALO active

Change-Id: Ib4226d021804900f0f922cf95bb2dd49696a0d6d
Fixes for clang:
PackageInfo is a class, not a struct.
String16 is contained in the android namespace. Do not namespace prefix it
within the android namespace.
Explicitly specify which std classes are necessary to prevent ambiguous
type errors. (map, set)

Change-Id: I0d01477a976e770821ebae8847f8d11b132a15d6