make skipping output optional

cmd/taler-auditor-offline-signing/main.go

@@ -679,7 +679,9 @@ func Sign(input *Input, skip map[SHA512Hash]bool, url string, pk ed25519.Private
 		hash, sig := SignDenom(&denom, sha512.Sum512(append([]byte(url), 0)), &input.Arguments.MasterPublicKey, &pk)
 
 		if skip[hash] {
+			if *verbose {
 				log.Printf("Skipping denom_pub_h %q as it has been already signed\n", hash)
+			}
 			continue
 		}
 
@@ -696,6 +698,7 @@ var (
 	injson  = flag.String("input", "-", "input json for signing")
 	keyfile = flag.String("key", "auditor.key", "filename of EC25519 private key")
 	url     = flag.String("url", "https://auditor.codeblau.de/", "auditor url")
+	verbose = flag.Bool("v", false, "verbose output on stderr")
 )
 
 func main() {