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: f68c6b3b1dcd5d00a2560c384475aaef3bc99487@10345 af82e41b-90c4-0310-8c96-b1721e28e2e2

dafrito/trac-mirror,dafrito/trac-mirror,dafrito/trac-mirror,dafrito/trac-mirror