extensible diff interface to adding/removing info (duplicate) fields #110
Description
The diff interface wants objects to have the exact same list of info keys before the diff can be computed. We should be able to support different lists of keys by just having a way to say (key,NULL,newvalue) for adding a keypair or (key,oldvalue,NULL) for removing a keypair.
Also, if the same key appears twice, only the first keypair one can be replaced. We could add an index to specify if the diff applies to the first or the second matching keypair.
Not critical at all, but better documented here than in my TODO list.