[BUG] Nested document validation is broken

Nested document validation seems to be broken in master branch. After a bit of debugging it seems that this is due to the fact that self.document attribute of subdocument validators gets assigned with a copy of the contents of the parent document (context) causing further validation steps to fail.

To reproduce

import cerberus

schema = {
    'info': {
        'type': 'dict',
        'schema': {
            'name': {'type': 'string', 'required': True}
        }
    }
}

validator = cerberus.Validator(schema)
res = validator.validate({'info': {'name': 'my name'}})
if not res:
    print validator._errors

[funkyfuture]

hm, this doesn’t fail.

what’s actually the output of your code above?

[funkyfuture]

that’s a nasty one, see #111 for some progress.