Cannot add ContributionType without also adding a display name

[zerocrates]

Imported from Trac ticket #158 reported by jboggs on 2011-02-17:

The add new ContributionType form indicates that users should be able to add a new type without filling out the Display Name field. In such a case, the Item Type name would be used. But the following error occurs when trying to add a type without a Display Name.

Display Name: You must provide a display name.