Maybe a bad git merge - not sure.
In any event, I do miss the trybots.

Noticed while fixing: change print-to-stderr+panic
to pure panic, just so that the test (which catches the panic)
does not print any errors before passing.

Change-Id: If25153ea64e81066455401110ae7a79c36f2f712
Reviewed-on: https://go-review.googlesource.com/78316
Run-TryBot: Russ Cox <rsc@golang.org>
Reviewed-by: Russ Cox <rsc@golang.org>