net/http: explain the "1.1" in the default User-Agent

R=golang-dev, adg
CC=golang-dev
https://codereview.appspot.com/13263052
undo CL 13348045 / 43675523c526

There is no reason to do this, and it's more work.

??? original CL description
net: make channel-based semaphore depend on receive, not send

R=r, dvyukov
CC=golang-dev
https://codereview.appspot.com/13348045

Committer: Rob Pike <r@golang.org>
???

R=golang-dev, r
CC=golang-dev
https://codereview.appspot.com/13632047