Fix taint and nesting bugs.

Tainted events should still be processed, even if we don't bother
the developer with the details.

The check for nested calls to the event verifier must incorporate
the event type because different event types might be overridden
in different subclasses so the nesting depths may vary.

Change-Id: If2fb213e07db783a0bd1da97bb12aad93126d712