Fix saving buffers with charsets other than utf-8 while using multi

This will also improve pipelinening for buffers and fixes the return value of Batch.exec

Fixes #913

test/helper.js

@@ -156,7 +156,9 @@ module.exports = {
             i++;
             if (i === max) {
                 func();
+                return true;
             }
+            return false;
         };
     },
     killConnection: function (client) {