string1.go contents are appended to string.go as is

Updates #12952

Change-Id: I30083ba7fdd362d4421e964a494c76ca865bedc2
Reviewed-on: https://go-review.googlesource.com/15951Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>