cookie: fix tailmatching to prevent cross-domain leakage

Cookies set for 'example.com' could accidentaly also be sent by libcurl
to the 'bexample.com' (ie with a prefix to the first domain name).

This is a security vulnerabilty, CVE-2013-1944.

Bug: http://curl.haxx.se/docs/adv_20130412.html
void Curl_cookie_clearall(struct CookieInfo *cookies)
{
  if(cookies) {
    Curl_cookie_freelist(cookies->cookies, TRUE);
    cookies->cookies = NULL;
    cookies->numcookies = 0;
  }
}

void Curl_cookie_clearall(struct CookieInfo *cookies)
{
  if(cookies) {
    Curl_cookie_freelist(cookies->cookies, TRUE);
    cookies->cookies = NULL;
    cookies->numcookies = 0;
  }
}
