Test-case for #164, ValidationError.__unicode__(): use 'is' operator instead of '==' for unset-check
Test-case for #164, ValidationError.__unicode__(): use 'is' operator
instead of '==' for unset-check

Currently test-case FAILS with a json-instances that have a screaming
__eq__() operator.

Julian/jsonschema,varunarya10/jsonschema,eodolphi/jsonschema,dnephin/jsonschema,mathewmarcus/jsonschema,eodolphi/jsonschema,sightmachine/jsonschema,jamesmarva/jsonschema,python-jsonschema/jsonschema,Julian/jsonschema