more generator spring cleaning

lib/6to5/types/builder-keys.json

@@ -19,6 +19,7 @@
   "Property":                ["kind", "key", "value", "computed"],
   "ReturnStatement":         ["argument"],
   "SequenceExpression":      ["expressions"],
+  "ThrowExpression":         ["argument"],
   "UnaryExpression":         ["operator", "argument", "prefix"],
   "VariableDeclaration":     ["kind", "declarations"],
   "VariableDeclarator":      ["id", "init"],

lib/6to5/types/index.js

@@ -50,6 +50,12 @@ _.each(_aliases, function (types, type) {
 
 //
 
+t.isExpression = function (node) {
+  return !t.isDeclaration(node);
+};
+
+//
+
 t.shallowEqual = function (actual, expected) {
   var same = true;