Implement "createIndex" via "ensureIndex"

Using arrays instead hash will will make better ordering of indexes
"collection.ensureIndex([["firstname", 1], ["lastname", 1]], callback)"

Author: slonofanya

lib/mongoHandler.js

@@ -147,19 +147,20 @@ MongoStore._unknownError = function(err) {
   };
 };
 
-
 MongoStore.prototype._createIndexesForRelationships = function(collection, relationshipAttributeNames) {
+  if (!(relationshipAttributeNames instanceof Array) || !relationshipAttributeNames.length) { return }
+
   var index = relationshipAttributeNames.reduce(function(partialIndex, name) {
-    partialIndex[name + ".id"] = 1;
+    if (name) {
+      partialIndex.push([name + ".id", 1]);
+    }
+
     return partialIndex;
-  }, {});
+  }, []);
 
-  if (Object.keys(index).length) {
-    collection.createIndex(index);
-  }
+  collection.ensureIndex(index);
 };
 
-
 MongoStore.prototype._applySort = function(request, cursor) {
   if (!request.params.sort) return cursor;