Fix bug where home presses were not poking user activity.

We now poke user activity twice: once upon dequeueing an event
for dispatch and then again just before we dispatch it.  The second
poke is to compensate for the fact that it can take a few seconds to
identify the dispatch target (if the application is responding slowly)
but we want to keep the display from going to sleep for X amount of time
after the app gets a chance to actually receive the event.  This mirrors
pre-Gingerbread behavior.

Removed some unnecessary code that filters user activity pokes when sending
events to KeyGuard.  We don't need this because KeyGuard already tells the
power manager to disable user activity.

Bug: 3101397
Change-Id: I8c3a77601fdef8f584e84cfdd11aa79da0ff51db