Add support for already decoded datetime/bool val
Add support for already decoded datetime/bool val

Formalchemy currently fails to validate already
decoded/deserialized boolean or datetime values, which
causes issues when input data was previously decoded
by the python json module.

camptocamp/formalchemy,camptocamp/formalchemy,FormAlchemy/formalchemy,camptocamp/formalchemy,FormAlchemy/formalchemy,FormAlchemy/formalchemy,FormAlchemy/formalchemy,camptocamp/formalchemy