With (Contract JARs) rolling upgrades the downgrade rule cannot be effectively check as the platform can't tell the difference between a transaction that's downgrading because of an attack, vs a transaction that's downgrading because Alice has upgraded but Bob hasn't yet. During a rolling upgrade we would expect state versions to fluctuate up and down as data gets read/written by a mix of nodes. With the feature as implemented Alice will upgrade and start trading with Bob. Bob will be able to read and process the states Alice sent him, but the moment he tries to consume such a state he will fail. This will result in cascading flow deaths and a hung business network the moment an upgrade starts.
This removes the need for the shareParentSessions parameter of FlowLogic.subFlow. It also has the flow's version number so FlowVersion is now no longer needed.
Core flows, which are baked into the platform, are also versioned using the platform version of the node. Several core flows, such as the data vending ones, which were provided via plugins are now instead baked into the node.
