additional_schemata changed to additionalSchemata

additional_schemata property changed to additionalSchemata in plone.autoform:
https://github.com/plone/plone.autoform/blob/e215744bce9d776dcdd77e340dc6a85554e0b511/CHANGES.rst#10b2---2009-07-12
Merge pull request #117 from Adniel/master

additional_schemata changed to additionalSchemata