NODE-950 modified the index generation as suggested by Matt

Author: christkv

lib/bulk/unordered.js

@@ -178,20 +178,18 @@ var addToOperationsList = function(_self, docType, document) {
   }
 
   // We have an array of documents
-  var insertIndex;
   if(Array.isArray(document)) {
     throw toError("operation passed in cannot be an Array");
   } else {
     _self.s.currentBatch.operations.push(document);
     _self.s.currentBatch.originalIndexes.push(_self.s.currentIndex);
-    insertIndex = _self.s.currentIndex;
     _self.s.currentIndex = _self.s.currentIndex + 1;
   }
 
   // Save back the current Batch to the right type
   if(docType == common.INSERT) {
     _self.s.currentInsertBatch = _self.s.currentBatch;
-    _self.s.bulkResult.insertedIds.push({index: insertIndex, _id: document._id});
+    _self.s.bulkResult.insertedIds.push({index: _self.s.bulkResult.insertedIds.length, _id: document._id});
   } else if(docType == common.UPDATE) {
     _self.s.currentUpdateBatch = _self.s.currentBatch;
   } else if(docType == common.REMOVE) {