Merge pull request #4340 from meonkeys/remove-ensureIndex-safe-option

don't add {safe:true} to MongoDB indexes

packages/mongo/mongo_driver.js

@@ -781,7 +781,6 @@ MongoConnection.prototype.findOne = function (collection_name, selector,
 MongoConnection.prototype._ensureIndex = function (collectionName, index,
                                                    options) {
   var self = this;
-  options = _.extend({safe: true}, options);
 
   // We expect this function to be called at startup, not from within a method,
   // so we don't interact with the write fence.