[PATCH] Add auth_param request_format, request_realm to proxy authentication schemes

Hi all,

The attached patch add the "auth_param request_format" and "auth_param
request_realm" to proxy authentication schemes.

The request_format value used to define the format of the helper request
line. It is a "quoted string" with logformat %macro support. A new
%credentials macro can be used to supply user password and other
scheme-dependent information to the helper.

The request_realm is an authenticated users cache key format, needed
when request_format feature is used to authenticate different users with
identical user names (e.g., when user authentication depends on http_port).

The Format::Format class used to produce the helper request line. This
class requires the AccessLogEntry, so passing this class to various
squid subsystems required.

Also this patch try to fill AccessLogEntry::cache::caddr (%>A) and
AccessLogEntry::cache::port (%la, %lp) members at the time the
AccessLogEntry build, instead of computing them just before the request
logged, to make them available for Format::Format class.

Regards,
   Christos