This patch removes the processing of `mxb' parameters in Accept headers in mod_negotiation. A second patch updates the manual to reflect this (mxb is not documented directly in the manual but support for it is implied in one place).
Reasons for removing this feature:
1) As currently implemented, the 'mxb' feature makes possible certain denial-of-service attacks on negotiated content. These attacks are posssible for user communities which access an Apache server from behind a HTTP/1.1 proxy which implements `Vary' related optimisations. Plugging this denial of service hole without removing `mxb' is fairly expensive in terms of degrading caching efficiency.
2) `mxb' is not in HTTP/1.0 or HTTP/1.1 or any other standard
3) Nobody seems to make use of 'mxb'. (Balachander Krishnamurthy kindly offered to grep some of his web traffic traces -- he did not find a single Accept with mxb in a whole day of recent traffic, nor in older traces)
4) Removing a feature makes a nice change from adding features.