Use url-domsuf.el if available

[Katsumi Yamaoka <yamaoka@xxxxxxx>]

Hi,

Now w3m-cookie.el uses url-domsuf.el (Lars wrote) that is available
in Emacs 24.3 or greater.  It provides the function
`url-domsuf-cookie-allowed-p' that checks if a domain is unique
to allow having cookies set.  It is much better than checking if
a domain matches `w3m-cookie-two-dot-domains-regexp'.  Formerly

(w3m-cookie-1-acceptable-p "ch.nicovideo.jp" ".nicovideo.jp")

returned nil, as it did not recognize ".nicovideo.jp" is a unique
domain name (at the era when w3m-cookie.el was written, a domain
name in Japan consisted of "FOO.co.jp", "BAR.go.jp", etc.).  Now
it returns t, and emacs-w3m will handle cookies for such sites
properly.

Regards,