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: eda3d06fcef731589ace1b284159cead3416df9b@10345 af82e41b-90c4-0310-8c96-b1721e28e2e2

jun66j5/trac-ja,jun66j5/trac-ja,jun66j5/trac-ja,netjunki/trac-Pygit2,walty8/trac,netjunki/trac-Pygit2,walty8/trac,walty8/trac,netjunki/trac-Pygit2,jun66j5/trac-ja,walty8/trac