[MERGE] bug1208

3.1 port of Internal Redirector feature Originally by Gonzalo Arana

Internal redirect support in squid3 would make live much easier for us, squid
redirection users.

squid.conf new directives:

url_map_access allow|deny acl-name [acl-name [acl-name ...] ]
url_map_access allow|deny acl-name [acl-name [acl-name ...] ]

ul_map new-url acl-name [acl-name [acl-name ...] ]

where 'new-url' format codes will be:

  %[#]formatcode

  '#' means URL quoted (%hex representation of non-alphanumeric characters).

%>a Client source IP address
%la Local IP address (http_port)
%lp Local port number (http_port)
%ts Seconds since epoch
%tu subsecond time (milliseconds, %03d)
%un User name
%ul User login
%ui User ident
%ue User from external acl
%rm Request method (GET/POST etc)
%ru Request URL
%rp Request path
%rh Request host from URL
%rH Request Host header
%rP Request protocol
%et Tag returned by external acl
%ea Log string returned by external acl
%% a literal % character

This port alters:
 - Directive names to 'url_map' and 'url_map_access' which better describe
   their actions (mapping URL to another form in transit).
 - Adds the --enable-url-maps configure option
 - Moves global API objects into a feature-specific header

It also polishes the makefiles slightly by grouping all redirection files
together nicely to reduce code duplication.