upgrade: register all format variants in a list...
upgrade: register all format variants in a list
Now that all known format variants exists outside of the function, we can gather
them in a lists. This build a single entry point other code can use (current
target: extensions).
The repository upgrade code is updated to simply use entries from this list.
As a side effect this will also allow extensions to register their own format
variants, to do this "properly" we should introduce a "registrar" for this
category of object. However I prefer to keep this series simple, and that will
be adventure for future time.