Resolve IPv4 addresses only for now.
Resolve IPv4 addresses only for now.

Makes Go 1.5 happy, and fixes #153.

DroiTaipei/mgo,DroiTaipei/mgo,jackspirou/mgo,Yottaa/mgo.v2,jjz/mgo,Yottaa/mgo.v2,hexadecy/mgo,gabrielrussell/mgo,jjz/mgo,hexadecy/mgo,jjz/mgo,deafgoat/mgo,hexadecy/mgo,jackspirou/mgo,DroiTaipei/mgo,lucasjo/mgo,gabrielrussell/mgo,lucasjo/mgo,go-mgo/travis-test,go-mgo/travis-test,deafgoat/mgo,go-mgo/travis-test,jackspirou/mgo,deafgoat/mgo,jackspirou/mgo,deafgoat/mgo,lucasjo/mgo,hexadecy/mgo,jjz/mgo,Yottaa/mgo.v2,lucasjo/mgo,go-mgo/travis-test,Yottaa/mgo.v2,gabrielrussell/mgo,gabrielrussell/mgo,DroiTaipei/mgo