Add new feature --is-state-compatible

[matthewdarwin]

Add new feature leap-util --is-state-compatible which returns either 0 or 1 exit code. This way the nodeos startup script could automatically use a snapshot if the existing saved state is not compatible. (eg upgrade from 4.0 to 5.0)

[bhazzard]

Thanks for the suggestion, we will consider this for a future version.

[bhazzard]

I think there might be an error code if state is not compatible. Is the issue that with heap mode that it wouldn't exit until all state is loaded into ram? And if so, is this moot because of the new mapped-private mode?