Further standardize RegXML type-vs-field interface

Also break out change types in rdifference.py.

Signed-off-by: Alex Nelson <a.nelson@prometheuscomputing.com>
Overhaul Registry value hashing

Signed-off-by: Alex Nelson <a.nelson@prometheuscomputing.com>
Remove an extra 'sys' import

Signed-off-by: Alex Nelson <a.nelson@prometheuscomputing.com>
Note imported Python revisions in ChangeLog