Array schema ref with required props

[natlibfi-arlehiko]

The following schema does not work:

1. A property references a schema which resolves to an array type
2. The array items is a reference to a inner definition
3. The definition resolves to an object which has mandatory properties

Instead of returning a formatted error JJVE throws an exception: TypeError: Cannot read property 'type' of undefined.

My workaround for this bug is to replace the references in the schema with the actual sub-schemas:

env.addSchema('foo', schema_foo);

errors = env.validate(schema, data);

if (errors) {
  schema.properties.foo = schema_foo;
  throw new Error(je(schema, data, errors);
}

[natlibfi-arlehiko]

PR #13 provides a test for this issue.