credit_only credits forwarding (#6509)

* credit_only_credits_forwarding

* whack transfer_now()

* fixup

* bench should retry the airdrop TX

* fixup

* try to make bench-exchange a bit more robust, informative

ledger/src/snapshot_utils.rs

@@ -87,7 +87,7 @@ pub fn package_snapshot<P: AsRef<Path>, Q: AsRef<Path>>(
         .rc
         .get_storage_entries()
         .into_iter()
-        .filter(|x| x.fork_id() <= bank.slot())
+        .filter(|x| x.slot_id() <= bank.slot())
         .collect();
 
     // Create a snapshot package