nsIDOMToString Interface

 The sole purpose of this interface is to make it easy for XPCOM
 object's to hook into JS' toString() when interacting with
 XPConnect. If you implement this interface and advertize it in the
 object's classinfo, you'll get automatic mapping from JS'
 toString() to the toString() method in this interface.

 XXXjst: This doesn't really belong in dom/public/idl/storage, but
 it gets to live here until I find a more suitable place.