Ensure we support legacy, maven-metadata.xml-only Maven packages

See several old packages. These are oddities without a POM, but just a maven-metadata.xml file. Many of these are peculiar as their file date is 2005-09-20 ... which is about the time of Maven 2/ POM3 release https://en.wikipedia.org/wiki/Apache_Maven#History

- https://repo.maven.apache.org/maven2/opensymphony/oscache/2.0.2/ only meta
- https://repo.maven.apache.org/maven2/abbot/abbot/0.12.3/ with a combo POM and meta
- https://repo.maven.apache.org/maven2/activesoap/jaxb-impl/20050407/ with a combo POM and meta
- https://repo.maven.apache.org/maven2/avalon/avalon-framework/4.1.4/ with a combo POM and meta