add some tests to be sure that the sample data is valid (marshal then unmarshal, vice-versa)

Conflicts:
	core/test-api/xml/src/main/java/org/opennms/core/test/xml/XmlTest.java
backport other xml test changes to 1.12
handle equality tests depth-first so we can tell where failures are
Merge remote-tracking branch 'origin/1.12'

Conflicts:
	core/test-api/xml/src/main/java/org/opennms/core/test/xml/XmlTest.java