Show error dialogs over apps that dismiss keyguard

Error dialogs absorb all input to ensure that they are not missed.
This can cause the screen to lock up if they are not displayed but
are still absorbing touches. This was what was happening when there
was an error dialog up at the same time as a phone call came in as
in b/17648830.

This fix recognizes when an app is dismissing the keyguard and
forces any error dialogs to be shown over such an app.

This also removes the private flags from the input system as they
are no longer needed.

Fixes bug 17648830.

Change-Id: I5c98b8265a1448b445fdb2f745fc78892f8656a4