[foreign] RFR duplicates in named layouts have to be reported as error

[Sundararajan Athijegannathan]

If same name is used for two different (group) layouts, LayoutResolver 
should detect and report error. But different header file interfaces can 
use the same name.

This is implemented by making LayoutResolver as a ClassValue rather than 
global.

Webrev: 
http://cr.openjdk.java.net/~sundar/redefinition_in_named_layouts/webrev.00/

Thanks,
-Sundar