vt: add an event interface

This is needed and requested in various forms for ConsoleKit, screenblank
handling and the like so do the job with a single interface. Also build the
interface so that unlike VT_WAITACTIVE and friends it won't miss events.

FIXME: Should this be a waitactive ioctl or a new device file you can poll
and read events from. We need the code anyway to fix up the existing broken
wait for console switch logic but the ConsoleKit people would prefer the
new device to the ioctl we have here

Signed-off-by: Alan Cox <alan@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>