Medium Description
RFC7950 specifies requirements for interoperability between RFC6020 and RFC7950 models:
A YANG version 1.1 module MUST NOT include a YANG version 1 submodule, and a YANG version 1 module MUST NOT include a YANG version 1.1 submodule. A YANG version 1 module or submodule MUST NOT import a YANG version 1.1 module by revision. A YANG version 1.1 module or submodule MAY import a YANG version 1 module by revision.
Add the corresponding checks and test suite so we enforce MUST NOTs as appropriate.