added a warning about reusing config objects to the config docs and to the Client constructor

src/lib/client.js

@@ -32,6 +32,13 @@ var _ = require('./utils');
 function Client(config) {
   config = config || {};
 
+  if (config.__reused) {
+    throw new Error('Do not reuse objects to configure the elasticsearch Client class: ' +
+      'https://github.com/elasticsearch/elasticsearch-js/issues/33');
+  } else {
+    config.__reused = true;
+  }
+
   function EsApiClient() {
     // our client will log minimally by default
     if (!config.hasOwnProperty('log')) {