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
test1218: another cookie tailmatch test

... and make 1216 also verify it with a file input

These tests verify commit 3604fde3d3c9b0d, the fix for the "cookie
domain tailmatch" vulnerability. See
http://curl.haxx.se/docs/adv_20130412.html
RELEASE-NOTES: cleaned up for 7.30 (synced with 5c5e1a1cd20)

Most notable the security advisory:
http://curl.haxx.se/docs/adv_20130412.html