Remove unnecessary locking for screen broadcasts.

The actual handling occurs in updateScreenOn() on the other side of a
handler, which acquires the lock correctly.

Change-Id: Ibd359446dba8e88f81d34f1e10a6b5e150348f89
Return error upon attempt to use non-existent APN

startUsingNetworkFeature will ignore errors from
reconnect - causing ConnectivityService to send
faulty information back to requester.

Change-Id: I4e0fcc1addd84da409cdc1eed1a95d25d925e020
Fix DateUtils.formatElapsedTime.

More reuse of StringBuilders, less broken home-grown formatting code.

Long-term, we should hand this over to icu4c, but they're not ready yet.

Bug: http://code.google.com/p/android/issues/detail?id=41401
Bug: 7736688
Change-Id: Ib3c1e1aad05827df646aa18645cce19dffb7551f
avoid crashing system serer process

Context#unregisterReceiver will throw IllegalArgumentException
if the receiver has already unregistered.

In GlobalAction class, when SilentModeAction is changed, it will
close the dialog with some delay. So there is a possibility
that it would unregistere again for the same receiver if a user
changes slient mode againand again. System must not crash in such
a case.

Change-Id: I33662feb48a770d39a8413901ec77ac1acd16bc7