RFR(XS): Fix issue with "8199852: Print more information about class loaders in LinkageErrors."

[Lindenmaier, Goetz]

Hi,

Unfortunately I need to do a small follow up for my LinkageError change.
If parentNameOop is NULL, parentName remains NULL. It should be set to <unnamed>. 
I actually saw a crash on solaris x86_64 with this.
I also remove some dead, leftover variables.

Please review:
http://cr.openjdk.java.net/~goetz/wr18/8203400-exMsg-fixLinkageError/01/

Best regards,
  Goetz.