Fixes #7782
Fixes #9554
Updates #7237 (original metabug, before we switched to specific bugs)
Updates #11932 (plan9 still doesn't have net I/O deadline support)

Change-Id: I96f311b88b1501d884ebc008fd31ad2cf1e16d75
Reviewed-on: https://go-review.googlesource.com/15941Reviewed-by: Ian Lance Taylor <iant@golang.org>
Reviewed-by: David du Colombier <0intro@gmail.com>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>