Review request for 8027020: [regression] java.lang.VerifyError: Bad type on operand stack

[A. Sundararajan]

Please review http://cr.openjdk.java.net/~sundar/8027020/
Bug: https://bugs.openjdk.java.net/browse/JDK-8027020
This fix is by Tomáš Hůrka

Background: In NB scenarios, it is possible to load nashorn classes from 
another *jar*. This fix makes sure that nashorn classes are always 
loaded from nashorn.jar (of extension dir) from scriptloader. This fix 
is also safe in normal environments - as ScriptLoader just uses 
StructureLoader for nashorn classes.

-Sundar