Fix referencing properties by CURIE in export

[beckyjackson]

Resolves #721

• docs/ have been added/updated
• tests have been added/updated
• mvn verify says all tests pass
• mvn site says all JavaDocs correct
• CHANGELOG.md has been updated

Change to compare IRI with equals() instead of == in export in order to allow both CURIEs and labels in export headers. I have no idea why two properties with the same IRI would be considered different IRI objects when we pass CURIEs but not labels, but if we change to this comparison, it's resolved.

Previously:

prop1.getIRI() == prop2.getIRI()

Now:

prop1.getIRI().equals(prop2.getIRI())

I also made the process to get the IRI of a header a little bit smarter.

[balhoff]

@beckyjackson how about prop1.getIRI().equals(prop2.getIRI())? .equals vs. ==

[beckyjackson]

I should have thought to try that first. It seems to work just as well.

It's strange that == works for by-label but not by-CURIE, but equals() works for all so... I won't question it.

[balhoff]

It's strange that == works for by-label but not by-CURIE, but equals() works for all so... I won't question it.

😄 strings may be reused internally I think (interned). Also OWL API uses a cache for the strings in IRI construction: https://github.com/owlcs/owlapi/blob/23593593c2853006bfe3bb61ec03fae2e3736461/api/src/main/java/org/semanticweb/owlapi/model/IRI.java#L63

I would just stick to .equals 99.999% of the time in Java. One of the little benefits of Scala is that the've swapped this and use == as value equality, and eq for object identity.