[JAXB-942] Consider namespace as publicId when resolving imported schemas.

This is a fix for [JAXB-942](https://java.net/jira/browse/JAXB-942).
Namespace of the imported schema will be used as publicid when trying to resolve this schema with the catalog/entity resolver. This is ths same logic which is used while schema parsing in case binding files are not specified.
I've tested all the combinations with/without `-nv` and `-b`, works fine.