Use proper exchange preparator (benchmark)

src/benchmark/taler-exchange-benchmark-new.c

@@ -78,6 +78,11 @@ enum BenchmarkError {
      USER_LOGIN_NAME, USER_LOGIN_PASS, EXCHANGE_URL)
 
 
+/**
+ * Exchange URL; never used, just needed by exchange preparator.
+ */
+static char *exchange_url;
+
 /**
  * Time snapshot taken right before executing the CMDs.
  */
@@ -403,6 +408,9 @@ main (int argc,
     return MISSING_BANK_URL;
   }
 
+  GNUNET_assert (GNUNET_OK == TALER_TESTING_prepare_exchange
+    (cfg_filename,
+     &exchange_url)); // never used, we do all via handle.
   result = TALER_TESTING_setup_with_exchange
     (run,
      NULL,