…en earlier

The aLongTimeAgo time value in net and net/http is used to cancel
in-flight read and writes. It was set to time.Unix(233431200, 0)
which seemed like far enough in the past.

But Raspberry Pis, lacking a real time clock, had to spoil the fun and
boot in 1970 at the Unix epoch time, breaking assumptions in net and
net/http.

So change aLongTimeAgo to time.Unix(1, 0), which seems like the
earliest safe value. I don't trust subsecond values on all operating
systems, and I don't trust the Unix zero time. The Raspberry Pis do
advance their clock at least. And the reported problem was that Hijack
on a ResponseWriter hung forever, waiting for the connection read
operation to finish. So now, even if kernel + userspace boots in under
a second (unlikely), the Hijack will just have to wait for up to a
second.

Updates #19747
Fixes #19771 (backport to Go 1.8.x)

Change-Id: Id59430de2e7b5b5117d4903a788863e9d344e53a
Reviewed-on: https://go-review.googlesource.com/38785
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Russ Cox <rsc@golang.org>
(cherry picked from commit e83fc2e44336423dab94bfe74fad4c4e6a4703b3)
Reviewed-on: https://go-review.googlesource.com/38786
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>