Wraps another Script instance in a WeakReference. Used to prevent a Tag class from holding a hard reference to its body script.
If the underlying Script has been GC'd and is no longer available, an exception is thrown on any attempt to use this Script.
WARNING: This class is not a permanent part of the API and will be removed or replaced in a future release. Don't extend it or use it unless you absolutely must.
@author Hans Gilde