RFR: 8062518: AIOBE occurs when accessing to document function in extended function in JAXP

[Aleksej Efimov]

Please, review the fix for the failure observed while accessing external 
document during xsl transformation: 
https://bugs.openjdk.java.net/browse/JDK-8062518
The jaxp code limits the access to external documents, but there is a 
possibility to access such documents from the xsl code - new regression 
test checks this functionality. The fix removes this restriction and 
AIOBE: http://cr.openjdk.java.net/~aefimov/8062518/9/webrev.00/

Testing:
xml related regression tests (with new test) - no failures (from jdk and 
jaxp repos).
JCK xml related tests - no failures.

With Best Regards,
Aleksej