net/http: ReadRequest doesn't populate req.Close

<pre>Example:
<a href="http://play.golang.org/p/rp28S9FqHx">http://play.golang.org/p/rp28S9FqHx</a>

I can work around this for now, but it's a bit annoying, especially since
transport.Roundtrip() only looks that the req.Close field and not any of the headers.</pre>
