Re: Sections 3.3.1 and 5.1

Actually, combining several suggestions and reducing redundancy,
I end up with the following:

"In requests that they forward, proxies MUST NOT rewrite the "abs_path"
part of a Request-URI in any way except as noted above to replace a
null abs_path with "*", no matter what the proxy does in its internal
implementation.

 Note: This rule ensures that the form of Request-URI is well
 specified, to enable future extensions without fear that they will
 break in the face of some rewritings. One consequence of rewriting the
 Request-URI is that integrity or authentication checks by the server
 may fail. Implementers should be aware that some pre-HTTP/1.1 proxies
 have been known to rewrite the Request-URI."
                                - Jim