John McCann points out via bugzilla that iptables happily accepts this
syntax on DNAT/SNAT:

	--to x.x.x.x:y:z

but doesn't actually make use of the second port.  Clear up the confusion
by only accepting a dash between the ports.

This closes bugzilla #265.

Phil

Signed-off-by: Phil Oester <kernel@linuxace.com>