Ok, it seems I forgot to clone the correct branch. 
Now after checking out the correct version, I was able to run the rake migrate without problems. 
But after restarting the server and trying to access redmine I get the following error: 

`ActionView::TemplateError (No plugin called 'redmine_status' - please use the full name of a loaded plugin.) on line #20 of app/views/layouts/base.rhtml:
17:       body {behavior: url(<%= stylesheet_path "csshover.htc" %>);}
18:     </style>
19: <![endif]-->
20: <%= call_hook :view_layouts_base_html_head %>
21: <!-- page specific tags -->
22: <%= yield :header_tags -%>
23: </head>

    lib/redmine/hook.rb:63:in `send'
    lib/redmine/hook.rb:63:in `call_hook'
    lib/redmine/hook.rb:63:in `each'
    lib/redmine/hook.rb:63:in `call_hook'
    lib/redmine/hook.rb:60:in `tap'
    lib/redmine/hook.rb:60:in `call_hook'
    lib/redmine/hook.rb:144:in `call_hook'
    app/views/layouts/base.rhtml:20:in `_run_rhtml_app47views47layouts47base46rhtml'
    /opt/passenger-3.0.8/lib/phusion_passenger/rack/request_handler.rb:96:in `process_request'
    /opt/passenger-3.0.8/lib/phusion_passenger/abstract_request_handler.rb:513:in `accept_and_process_next_request'
    /opt/passenger-3.0.8/lib/phusion_passenger/abstract_request_handler.rb:274:in `main_loop'
    /opt/passenger-3.0.8/lib/phusion_passenger/classic_rails/application_spawner.rb:321:in `start_request_handler'
    /opt/passenger-3.0.8/lib/phusion_passenger/classic_rails/application_spawner.rb:275:in `send'
    /opt/passenger-3.0.8/lib/phusion_passenger/classic_rails/application_spawner.rb:275:in `handle_spawn_application'
    /opt/passenger-3.0.8/lib/phusion_passenger/utils.rb:479:in `safe_fork'
    /opt/passenger-3.0.8/lib/phusion_passenger/classic_rails/application_spawner.rb:270:in `handle_spawn_application'
    /opt/passenger-3.0.8/lib/phusion_passenger/abstract_server.rb:357:in `__send__'
    /opt/passenger-3.0.8/lib/phusion_passenger/abstract_server.rb:357:in `server_main_loop'
    /opt/passenger-3.0.8/lib/phusion_passenger/abstract_server.rb:206:in `start_synchronously'
    /opt/passenger-3.0.8/lib/phusion_passenger/abstract_server.rb:180:in `start'
    /opt/passenger-3.0.8/lib/phusion_passenger/classic_rails/application_spawner.rb:149:in `start'
    /opt/passenger-3.0.8/lib/phusion_passenger/spawn_manager.rb:219:in `spawn_rails_application'
    /opt/passenger-3.0.8/lib/phusion_passenger/abstract_server_collection.rb:132:in `lookup_or_add'
    /opt/passenger-3.0.8/lib/phusion_passenger/spawn_manager.rb:214:in `spawn_rails_application'
    /opt/passenger-3.0.8/lib/phusion_passenger/abstract_server_collection.rb:82:in `synchronize'
    /opt/passenger-3.0.8/lib/phusion_passenger/abstract_server_collection.rb:79:in `synchronize'
    /opt/passenger-3.0.8/lib/phusion_passenger/spawn_manager.rb:213:in `spawn_rails_application'
    /opt/passenger-3.0.8/lib/phusion_passenger/spawn_manager.rb:132:in `spawn_application'
    /opt/passenger-3.0.8/lib/phusion_passenger/spawn_manager.rb:275:in `handle_spawn_application'
    /opt/passenger-3.0.8/lib/phusion_passenger/abstract_server.rb:357:in `__send__'
    /opt/passenger-3.0.8/lib/phusion_passenger/abstract_server.rb:357:in `server_main_loop'
    /opt/passenger-3.0.8/lib/phusion_passenger/abstract_server.rb:206:in `start_synchronously'
    /opt/passenger-3.0.8/helper-scripts/passenger-spawn-server:99

Rendering /srv/www/redmine.someurl.com/redmine/public/500.html (500 Internal Server Error)`