[PATCH] Add Max-Forwards: TRACE handling to proxy

[Martin Kraemer <Ma...@mch.sni.de>]

RFC2068 describes the Max-Forwards: header as a delimiting factor for a
proxy chain. It works only for the TRACE method. The appended patch
tries to implement it for Apache's proxy.

    Martin

___________from RFC2068:___________
14.31 Max-Forwards

   The Max-Forwards request-header field may be used with the TRACE
   method (section 14.31) to limit the number of proxies or gateways
   that can forward the request to the next inbound server. This can be
   useful when the client is attempting to trace a request chain which
   appears to be failing or looping in mid-chain.

	  Max-Forwards   = "Max-Forwards" ":" 1*DIGIT

   The Max-Forwards value is a decimal integer indicating the remaining
   number of times this request message may be forwarded.

   Each proxy or gateway recipient of a TRACE request containing a Max-
   Forwards header field SHOULD check and update its value prior to
   forwarding the request. If the received value is zero (0), the
   recipient SHOULD NOT forward the request; instead, it SHOULD respond
   as the final recipient with a 200 (OK) response containing the
   received request message as the response entity-body (as described in
   section 9.8). If the received Max-Forwards value is greater than
   zero, then the forwarded message SHOULD contain an updated Max-
   Forwards field with a value decremented by one (1).

   The Max-Forwards header field SHOULD be ignored for all other methods
   defined by this specification and for any extension methods for which
   it is not explicitly referred to as part of that method definition.
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