Validate change before reset

Dependencies

• [2] SXEYMYF7 Fixing the bad changes in history (unfortunately, by rebooting).

Change contents

• replacement in pijul/src/commands/reset.rs at line 28
  [2.98558]→[2.98558:98600](∅→∅)
  − } else if self.change.is_some() {
  [2.98558]

  [2.98600]
  + } else if let Some(ref chg) = self.change {

  + txn.hash_from_prefix(&chg)?;