+ (** parse 1st line of an HTTP request
+ @param inchan input channel from which parse request
+ @return a triple meth * url * version, meth is the HTTP method invoked, url is
+ the requested url, version is the HTTP version specified or None if no version
+ was specified
+ @raise Malformed_request if request 1st linst isn't well formed
+ @raise Malformed_request_URI if requested URI isn't well formed *)