[krbdev.mit.edu #7686] Master key rollover mishandles databases created prior to 1.7

[Greg Hudson via RT]

Contrary to the initial description of this ticket, I did not change 
add_mkey to instantiate the master key activation list.  Instead, I 
changed the fallback list to emulate what would be in the list if the DB 
had been created after 1.7, and made the fallback list apply to all cases 
instead of just in kadmind.