our daffodil source tree has, intentionally, invalid DFDL schema files that cause validation to fail for unit test purposes (negative tests). We should rename these files so they don't cause the Eclipse (or other) IDE to create distracting validation warnings when you have the daffodil source tree open.

These tests need to explicitly use file names like foo.dfdl.xsd.invalid so that the IDE will not view it as a XSD file and try to validate it.

This will enable a single setup of Eclipse to be used by persons trying to author DFDL schemas, who want the XML & XSD validation capabilities turned on, and used by persons trying to do daffodil development.