upgrade: split some logic from UpgradeOperation...
upgrade: split some logic from UpgradeOperation
The logic for automatic-upgrade and the upgrade-repo should be able to use the
same code. However that code often need an UpgradeOperation object to function.
So we start spliting the Operation into a minimal component that we will be
able to reuse outside of the "classic" upgrade path.
We will put the base-class to use in the next changeset.
Differential Revision:
https://phab.mercurial-scm.org/D12612
