Revert the following change set:

        changeset:   13018:97d027b3aa68
        user:        Gustavo Niemeyer <gustavo@niemeyer.net>
        date:        Mon Apr 23 22:00:16 2012 -0300
        summary:     net/http: allow clients to disable keep-alive

This broke a test on Windows 64 and somebody else
will have to check.

R=golang-dev, r
CC=golang-dev
https://golang.org/cl/6112054