AbstractJcrNode Javadoc Throws Clause Are Out Of Sync

Some of the methods in AbstractJcrNode still have Javadoc for the UnsupportedOperationException that they used to throw. According to a quick text search of all the places where "@throws Unsupported" occurs in dna-jcr, this is the only file with this type of erroneous Javadoc.

I also marked off the getReferences method as it is not implemented per spec.