From https://github.com/golang/go/issues/11745#issuecomment-123555313
this implements option (b), having the server pause slightly after
sending the final response on a TCP connection when we're about to close
it when we know there's a request body outstanding. This biases the
client (which might not be Go) to prefer our response header over the
request body write error.

Updates #11745

Change-Id: I07cb0b74519d266c8049d9e0eb23a61304eedbf8
Reviewed-on: https://go-review.googlesource.com/12658Reviewed-by: Russ Cox <rsc@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>