fix #50: exit non-zero if some objects failed

main.go

@@ -201,6 +201,6 @@ func main() {
 
 	err := app.Run(os.Args)
 	if err != nil {
-		logger.Fatalf("Error running juicesync: %v", err.Error())
+		logger.Fatalf("Error running juicesync: %s", err)
 	}
 }

sync/sync.go

@@ -410,5 +410,8 @@ func Sync(src, dst object.ObjectStorage, config *config.Config) error {
 	}
 	doSync(src, dst, srcCh, dstCh, config)
 	logger.Infof("Found: %d, copied: %d, deleted: %d, failed: %d", found, copied, deleted, failed)
+	if failed > 0 {
+		return fmt.Errorf("Failed to copy %d objects", failed)
+	}
 	return nil
 }