If a multi update fails on one docs, the others shouldnt be changed

lib/datastore.js

@@ -427,12 +427,14 @@ Datastore.prototype._update = function (query, updateQuery, options, cb) {
       return callback(err);
     }
 	
+	// Change the docs in memory
 	try {
       self.updateIndexes(modifications);
 	} catch (err) {
 	  return callback(err);
 	}
 
+	// Update the datafile
     self.persistence.persistNewState(_.pluck(modifications, 'newDoc'), function (err) {
       if (err) { return callback(err); }
       return callback(null, numReplaced);