[foreign] RFR Cache binder generated classes with ClassValue

[Sundararajan Athijegannathan]

Please review: 
http://cr.openjdk.java.net/~sundar/binder_class_cache_cleanup/webrev.00/

* Binder generated classes are cached using two ClassValues - one for 
header impls and one for struct impls.

Other cleanups:

* Enabled those checks for annotations (NativeType, NativeHeader) in 
LibrariesHelper.

* generating default constructor so that we can avoid 
unsafe.allocateInstance() can be avoided to create bind instances.

* Using ArrayList instead of HashMap in BinderClassWriter. We don't need 
the keys and we just need to iterate the values.

Thanks,
-Sundar