Set Validation Error, empty value support for 2.0.x

Bug reports always have to go against the latest dev release and will then be back ported if necessary.

The code in 2.x contains everything from 1.2, but the problem wasn't properly solved there either. The field name can indeed be left empty as mentioned in the field description: "Leave empty to set a global error on the form."

The problem was, that the access control method didn't know about that special case and didn't allow for the empty field name. This should be fixed with the latest commit. Please test this out and set the issue to RTBC if it solves the problem. We can then back port and fix this.

Commit tested, both on the generic example listed above and a separate webform-based model. Both successfully set the validation error on the entire form without a field name listed.

Thanks @jwineichen

Automatically closed - issue fixed for 2 weeks with no activity.