message: Don't consider eras before activation points to be bonded.
  The upgrade or restart could have made changes to the validator set.
diff: @@ -1240,5 +1240,7 @@ fn bonded_eras(protocol_config: &ProtocolConfig) -> u64 {
  /// The oldest era whose validators are still bonded.
  // This is public because it's used in reactor::validator::tests.
  pub(crate) fn oldest_bonded_era(protocol_config: &ProtocolConfig, current_era: EraId) -> EraId {
  - current_era.saturating_sub(bonded_eras(protocol_config))
  + current_era
  + .saturating_sub(bonded_eras(protocol_config))
  + .max(protocol_config.last_activation_point)
  }
  