Major Description
There is an action to add a selected Model Extension Definition (MED) to the registry. This action is accessed from the Model Extension Registry View and from the MED Editor. If the user wants to update an existing MED in the registry the user must perform a delete and then an add.
The action should be changed to notice if the MED being registered is new or is one being updated. If it is an updated MED the user should be asked for overwrite confirmation. If the user tries to update a MED that is exactly equal to the registered MED the update should not occur and the user told why.
Since right now both the MED namespace prefix and namespace URI must be unique in the registry an interesting, and hopefully infrequent scenario can occur: both the namespace prefix and namespace URI of the MED being registered exist already in the registry but are found in different MEDs. Do we allow an update in this case?
