Second patch from issue2550688 -- with some changes: - password.py now has a second class JournalPassword used for journal storage. We have some backends that directly store serialized python objects. Also when reading from the journal some backends expected the string read to be usable as a parameter to a Password constructor. This now calls a JournalPassword constructor in all these cases. The new JournalPassword just keeps the scheme and has an empty password. - some factoring, move redundant implementation of "history" from rdbms_common and back_anydbm to hyperdb.