wp-test-lib submodule missing, makes submodule recursive update/init fail

Hi,

When I try to update all my project submodules, when it reaches the https://github.com/scribu/wp-tests-lib.git submodule of WPThumb the process asks for some user and pass. Putting the wrong one makes the process to fail, so I have to init/update all submodules on the same level manually.
Going to https://github.com/scribu/wp-tests-lib.git shows a Not Found page.