Commit cee110b2 (IPython Notebook: Fixing coding crimes for section
names) changed IPython notebook section name to use '-' as word
delimiter but forgot to update users, and this way wendelin build
started to fail:
INFO Getting section ipython_notebook.
INFO Error: The referenced section, 'ipython_notebook', was not defined.
Fix it. (And I've made sure with whole-tree git grep that there is no
more ipython notebook users except wendelin in whole slapos.git so far)