[krbdev.mit.edu #3583] DAL disables krb4 compat

[Ken Raeburn via RT]

One of the changes in the DAL integration disabled the ability to do  
krb4-style database loads and dumps.  This breaks the migration path  
for any sites still running Kerberos v4 only.  I hope there aren't  
any (maybe some AFS site?), but unless we make a conscious choice  
that we're going to punt any such sites now, this needs to be fixed.