More cookie fixes

 * Add some error handling in NetworkCookie and don't add broken cookies
(or should I say crumbs?) to the cookie jar
 * More control on the path and domain, as well as the expiration time

We now pass Opera cookie testsuite functionality tests, as well as some
of the negative tests (we even do better than curl). Not going further
right now as this works well enough for positive cases and most
security/privacy issues are fixed (cross domain and cross path cookie
setting or spying).