RFR [14/java.xml] 8068376: Validator fails valid XML files due to String == in XSD validator code

[Joe Wang]

Please review a quite fix in a validation source where a String 
comparison was made as references.

JBS: https://bugs.openjdk.java.net/browse/JDK-8068376
webrev: http://cr.openjdk.java.net/~joehw/jdk14/8068376/webrev/
Thanks,
Joe