8004371: (props) Properties.loadFromXML needs small footprint XML parser as fallback when JAXP is not present

[Alan Bateman]

I've refreshed the webrev here to take in another change from Joe to the 
root element handling in PropertiesDefaultHandler.

http://cr.openjdk.java.net/~alanb/8004371/webrev.03/

I'd like to get this into jdk8/tl in the next few days if possible.

On tests on then I've expanded LoadAndStoreXML to include a directory of 
invalid XML documents (those that should cause 
InvalidProperitesFormatException to be thrown) so that improves the test 
coverage a bit. Joe has several other tests in the works so I've 
suggested to him that he does a follow-up change in the coming weeks 
with those tests.

-Alan.