0.13dev: Only generate a new authentication cookie on `/login` if the user doesn't already provide a valid one. This should prevent the `auth_cookie` table from growing too much. Also, accept relative URLs as referrers.
0.13dev: Only generate a new authentication cookie on `/login` if the user doesn't already provide a valid one. This should prevent the `auth_cookie` table from growing too much. Also, accept relative URLs as referrers.

Part of #540.


git-svn-id: 0d96b0c1a6983ccc08b3732614f4d6bfcf9cbb42@10345 af82e41b-90c4-0310-8c96-b1721e28e2e2

rbaumg/trac,rbaumg/trac,rbaumg/trac,rbaumg/trac