crypto/tls: don't return an error from Close()
crypto/tls: don't return an error from Close()

Fixes issue 1037.

R=adg, rsc1
CC=golang-dev
http://codereview.appspot.com/2107048
abustany/go,abustany/go,abustany/go,abustany/go,abustany/go,abustany/go,abustany/go