Error on translating booleans

Hi,

First of all, I'm not sure if this is a bug on your part, so I apologize in advance if it isn't.

I was trying to translate a boolean field, but although the value is recorded correctly, when Symfony tries to retrieve the value, it throws me a TransformationFailedException when trying to do this:

`BooleanToStringTransformer ->transform ('1')`

Boolean/checkbox fields work different in forms, so I think it is necessary to cast the value before passing it to the form.

Thanks in advance.