TDML runner - throws exception if test has neither <tdml:errors> nor <tdml:infoset>

A TDML parserTestCase must contain a document (for the data), and either a tdml:errors for a negative test, or a tdml:infoset for a positive test case. If the test has neither, and is invoked from the CLI via 'daffodil test -iii my.tdml my_test' you get the "This is a bug" printout due to an abort.

The TDML is XML. Before we run it, it should be validated (by Xerces) and the XML schema for TDML should enforce that either tdml:errors or tdml:infoset is present, so that you get an invalid XML diagnostic message.