RFR [11] (JAXP): 6857903: SAXException.initCause() does not correctly set Exception

[Aleks Efimov]

Hello,

Please, help to review the fix for jaxp bug that fixes SAXException to 
correctly set exception cause with 'setCause' method:
http://cr.openjdk.java.net/~aefimov/6857903/dev/00/
I've tried to keep the fix miminal with respect to serial form of this 
API class, i.e. kept private 'exception' field.

The new test case was added to IssueTracker56Test unit test. Testing 
showed no related JCK/JTREG failures.

With Best Regards,
Aleksei