cmd/godoc: add support for doc.Package.Notes

Add support for displaying the notes of the form 'MARKER(userid): comment' now collected by the go/doc package. Any two or more uppercase letters are recognised as a marker.

R=gri, rsc, bradfitz
CC=golang-dev
https://codereview.appspot.com/7334044

Committer: Robert Griesemer <gri@golang.org>
runtime: expand error for signal received on non-Go thread.

We call runtime.findnull dynamically to avoid exceeding the
static nosplit stack limit check.  (Thanks minux!)

Fixes issue 4048.

R=rsc, minux.ma, ality
CC=golang-dev
https://codereview.appspot.com/7232066

Committer: Russ Cox <rsc@golang.org>