godoc: improved output of examples in html.
godoc: improved output of examples in html.

Fixes issue 2467.
Fixes issue 2464.

R=golang-dev, rsc, adg
CC=golang-dev
http://codereview.appspot.com/5447051

Committer: Andrew Gerrand <395a7d33bec8475c9b83b7d440f141bcbd994aa5@golang.org>

tav/go,tav/go,tav/go,tav/go,tav/go,tav/go,tav/go