Don't include flags in configuration change if their value hasn't changed.

This makes the check in updateFrom() match the logic in diff().

Change-Id: I3ab4e8460f7fbf985ef55b9514a8aa90d401d486
Fix notification LED sometimes being disabled by a missed phone call.

This was the case if there was a notification with LED pending prior to
the missed call. After the missed call, mLedNotification was still set
to the pending notification, but the force-with-screen-off flag was only
set on the missed call notification, which wasn't checked.
Fix that issue by always assigning the latest notification to
mLedNotification when the notification is enqueued. Make an exception if
the current notification is flagged for being forced at screen off and
the screen is currently on, otherwise there's a race condition where a
notification coming in while the screen is still on after a missed call
will cause the LED to be turned off at the time the screen is turned
off.

JIRA:CYAN-652
Change-Id: I1df0b40cca2af7a08c240677d22d2a95097b7184