Link module treats .asia as an invalid domain name

... but in fact, it should be valid.

I checked the list at http://www.iana.org/domains/root/db/ to see if there were others that might be missing, and the only one I found was .tel - however, that seems to be a particularly weird one according to http://en.wikipedia.org/wiki/.tel and might not be worth including? So for now, the attached patch just adds .asia to the list.