correct a little error in tutorial text
fix non-existent collaborator error
Merge pull request #305 from migeruhito/tutorial_typo

Problem with notebook's help
Fix typo that would cause crash

But only in the situation that one chose to do something the GUI doesn't support!  
Still worth it, though, and clear enough I'm not going to ask for review in this case.
Catch / in collaborators' names
Merge pull request #306 from migeruhito/collaborators

Crash when a non-existent collaborator is added to a worksheet