save more cookies between invocations

[Dan Jacobson]

Wishlist: giving a way to save the types of cookies you say you won't in:
`--save-cookies FILE'
     Save cookies to FILE at the end of session.  Cookies whose expiry
     time is not specified, or those that have already expired, are not
     saved.
so we can carry state between wget invocations, without having to dig
them out of -S output.  There should be several levels of saving
allowed, including overriding expiry dates, etc.