in context of erp5 site (not web_site), user were redirected to
/erp5/portal_password/login_form, so after sign in, they were redirected to
/erp5/portal_password which is wrong.

Following patch use came_from request variable and is compatible both with
 web_site and erp5 site.


git-svn-id: https://svn.erp5.org/repos/public/erp5/trunk@37835 20353a03-c40f-0410-a6d1-a30d3c3de9de