Make "empty patch" checking optional in "series"

Make "empty patch" checking optional in "series"

That's just too slow, and quilt doesn't do it, so user will live with it.
Don't know if there's a reason to allow dropping the fanciness here
entirely, but I think there's no user doing one-liner scripts with quilt
series. And anyway, for that you can do "stg applied; stg unapplied".

Actually, with this patch you must ask explicitly the checking.

Signed-off-by: Paolo 'Blaisorblade' Giarrusso <blaisorblade@yahoo.it>