Catch up with ports version 2.30:

If the user specified --no-confirm don't build the list. With a lot of
ports to update it can get quite large.

If there are a very large number of ports installed the grep in
iport_from_origin() can fail with "Argument list too long." It's also
theoretically possible that the grep would fail for other reasons. So
if it does, fall back to 'pkg_info -O'. My method is faster which is
why I'm still trying it first, but this is a sort of "belt and
suspenders" situation.