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
static bool tailmatch(const char *little, const char *bigone)
static bool tailmatch(const char *cooke_domain, const char *hostname)
 {
  size_t cookie_domain_len = strlen(cooke_domain);
  size_t hostname_len = strlen(hostname);
 
  if(hostname_len < cookie_domain_len)
     return FALSE;
 
  if(!Curl_raw_equal(cooke_domain, hostname+hostname_len-cookie_domain_len))
    return FALSE;

  /* A lead char of cookie_domain is not '.'.
     RFC6265 4.1.2.3. The Domain Attribute says:
       For example, if the value of the Domain attribute is
       "example.com", the user agent will include the cookie in the Cookie
       header when making HTTP requests to example.com, www.example.com, and
       www.corp.example.com.
   */
  if(hostname_len == cookie_domain_len)
    return TRUE;
  if('.' == *(hostname + hostname_len - cookie_domain_len - 1))
    return TRUE;
  return FALSE;
 }

static bool tailmatch(const char *little, const char *bigone)
 {
  size_t littlelen = strlen(little);
  size_t biglen = strlen(bigone);
 
  if(littlelen > biglen)
     return FALSE;
 
  return Curl_raw_equal(little, bigone+biglen-littlelen) ? TRUE : FALSE;
 }
