Multiple signatures for transactions

With multiple instructions in a TX may need
multiple signatures.

Fixes #1531

tests/programs.rs

@@ -43,7 +43,10 @@ fn create_bpf_path(name: &str) -> PathBuf {
 fn check_tx_results(bank: &Bank, tx: &Transaction, result: Vec<solana::bank::Result<()>>) {
     assert_eq!(result.len(), 1);
     assert_eq!(result[0], Ok(()));
-    assert_eq!(bank.get_signature(&tx.last_id, &tx.signature), Some(Ok(())));
+    assert_eq!(
+        bank.get_signature(&tx.last_id, &tx.signatures[0]),
+        Some(Ok(()))
+    );
 }
 
 struct Loader {