(ok 2.9.0) Save cookie name/password

Hi-

I have a pretty simple request for the cookie auth method: A pref
to customize expiration time of the cookies. Currently, the
password cookie expires when the browser is closed.

Some of us use PMA in a secure, intranet environment with
multiple servers and want the login to be valid for a fixed time.

So how about adding a pref allowing us to set that time? It took
me about 30 seconds to customize line 626 of cookie.auth.lib.php
but others might find this useful.

Thanks.