NAVL validation errors - Junk fields should be listed explicitly

[dread]

When you create a package, but specify a key that is not allowed (e.g. 'relationships') then you get error message:

{"__junk": ["The input field __junk was not expected."]}

It should mention the actual key which is not expected. e.g.

{"relationships": ["The input field 'relationships' was not expected."]}

Kindly said that James' version of NAVL was better in this respect, so this might be best solved by moving to that.