RFR (S) 8197780: Null pointer dereference in Klass::is_instance_klass of klass.hpp:532

[coleen.phillimore at oracle.com]

Summary: Make generate_class_cast_message able to deal with NULL klass 
from the constant pool.

Also moved the function to get the class loader/module name to Klass 
where it belongs and removed an unused function in the constant pool 
that looks like the one I ended up using.

Tested with tier1 and which includes the test added for the original 
change and compiler test that has null klass in the constant pool entry: 
compiler/escapeAnalysis/cr6716441/Tester.java

open webrev at http://cr.openjdk.java.net/~coleenp/8197780.01/webrev
bug link https://bugs.openjdk.java.net/browse/JDK-8197780

Thanks,
Coleen