spec: index of non-addressable array is not addressable
spec: index of non-addressable array is not addressable

Motivated by:

func f() []int
func g() [10]int

f()[1] = 1  // ok
g()[1] = 1 // ERROR

R=gri
CC=golang-dev
http://codereview.appspot.com/1278041
abustany/go,abustany/go,abustany/go,abustany/go,abustany/go,abustany/go,abustany/go