go spec: method names must be unique
go spec: method names must be unique

Fixes issue 2916.

R=golang-dev, remyoudompheng, r, rsc
CC=golang-dev
http://codereview.appspot.com/5652064
abustany/go,abustany/go,abustany/go,abustany/go,abustany/go,abustany/go,abustany/go