JDK 8 RFR 7179567: JCK8 tests: api/java_net/URLClassLoader/index.html#Ctor3 failed with NPE

[Brian Burkhalter]

Please review and comment at your convenience.

Issue:	https://bugs.openjdk.java.net/browse/JDK-7179567
Webrev:	http://cr.openjdk.java.net/~bpb/7179567/

Summary
* Document and throw IAE from URLClassLoader constructors.
* Throw ClassNotFoundException if null is passed to findClass method of a ClassLoader.
* Clarify specification of SecureClassLoader.getPermissions.

This change would require an approved CCC request and JCK test changes.

Thanks,

Brian