go spec: clarify return type of append, argument type for ...T parameters
go spec: clarify return type of append, argument type for ...T parameters

R=iant, ken2, r, rsc
CC=golang-dev
http://codereview.appspot.com/2774041
abustany/go,abustany/go,abustany/go,abustany/go,abustany/go,abustany/go,abustany/go