cmd/gc: fix escape analysis of method values

R=ken2
CC=golang-dev
https://codereview.appspot.com/7518050
crypto/tls: use method values

Currently fails with a compiler error, though.

R=golang-dev, agl, rsc
CC=golang-dev
https://codereview.appspot.com/7933043

Committer: Russ Cox <rsc@golang.org>