Get rid of Debianize' RetrieveMethod constructor and merge the DebSpec type into PackageFlags
Remove Cabal and add Zero to RetreiveMethod
Remove Eq instance from RetrieveMethod
Add the Debianize' constructor back and immediately convert it to Debianize when it is read
Add a Maybe String argument to Debianize, to set the source package name
Restore the backwards compatibility code for the Debianize RetrieveMethod