The new comparison rule was added to the spec by

	changeset:   5605:33abb649cb63
	user:        Robert Griesemer <gri@golang.org>
	date:        Thu Jun 03 16:55:50 2010 -0700
	files:       doc/go_spec.html
	description:
	go spec: Base comparison compatibility on assignment compatibility.

	Specifically:
	- Simplified definition of comparison compatibility and folded into
	  section on comparison operators since it's only used there.

	This is a small language change/cleanup. As a consequence:
	- An interface value may now be compared against a non-interface value.
	- Channels with opposite directions cannot be compared directly anymore
	  (per discussion with rsc).

	R=rsc, r, iant, ken2
	CC=golang-dev
	https://golang.org/cl/1462041

but never implemented.

Fixes #1070.

R=ken2
CC=golang-dev
https://golang.org/cl/2116047