Cookies

I made a few small changes to the cookie support
(mainly one change and a couple of utily function added).

First of all, I added a new CookieMode: HT_COOKIE_SAME_DOMAIN. It works
like HT_COOKIE_SAME_HOST but only checks for the terminal part of the
hostname (possibly the ___domain name).

This allows to accept/send cookies to all the hosts in the same ___domain,
since many sites now split their content on multiple hosts.

Also I added a couple of new string utilities: tailcomp and tailcasecomp.
They act like strcmp and strcasecmp but check the first strings against
the end of the second string. This allows "___domain comparison" as described
in the cookie specs.

The code is still missing all the checks for a proper ___domain (2 or 3 dots
depending on the top level), but it's ok for controlled use.

If you think this code can be useful I can check it in.

-- Raffaele