Issue 166: clarify term "User Agent" and resolve inconsistencies with W3C specs

Hi,

based on an off-list suggestion from Larry, I just added 
<http://trac.tools.ietf.org/wg/httpbis/trac/ticket/166>.

Larry Masinter wrote:
> Brief summary:
> 
> The HTTP document uses two terms "user agent" and "client",
> and in some cases it is careful to distinguish between them,
> but not always. I would like to see a careful
> review of each appearance of the terms to insure that
> "user agent" is used in situations where there is a user,
> and "client" used in cases where the initiator of the action
> is either a user agent or another agent with no explicit user.
> 
> I think this will help the document, and the task relatively
> limited and editorial.
> 
> Some instances may require discussion.
> 
> Larry
> --
> http://larry.masinter.net

BR, Julian