PlaybookInclude does not support vars_files

Hello,

In Ansible 2.0, PlaybookInclude [1] does not support vars_files attribute. But vars attribute is supported. Is this a feature change from 1.9 to 2.0 or is it a mistake?

Sample Code:

vars_files.yml
`

2.0 is now strict and reports many incorrect syntax constructs that were previously just ignored and skipped.