TDMLRunner not detecting tdml:defineConfig's with same name

It looks like the TDMLRunner does not detect and error if duplicate defineConfigs exist. For example, the config "cfg_defaultNamespace" is defined twice in this file with different tuanble settings.

daffodil-test/src/test/resources/org/apache/daffodil/section00/general/tunables.tdml

This likely means someone copy/pasted a config and forgot to change the name, so there are probably tests not using the intended configs. We added the capability to detect and error when test cases are defined with duplicate names. We should probably do the same for defineConfig.