Support for type aliases inside ambient module declarations. microsoft/TypeScript#3004

Author: sedwards2009

test.ts

@@ -302,6 +302,12 @@ export function testTypeAlias2(test: nodeunit.Test): void {
   roundTrip(test, `type strings = string|string[];`);
 }
 
+export function testTypeAliasInModule(test: nodeunit.Test): void {
+  roundTrip(test, `declare module "foo" {
+  type strings = string|string[];
+}`);
+}
+
 export function testImportDeclaration(test: nodeunit.Test): void {
   roundTrip(test, `import foo = bar;`);
 }

typescript_definition.pegjs

@@ -778,13 +778,15 @@ ambient_module_element
     / EXPORT __ result:ambient_enum_declaration { result.export = true; return result; }
     / EXPORT __ result:ambient_module_declaration { result.export = true; return result; }
     / EXPORT __ result:import_declaration { result.export = true; return result; }
+    / EXPORT __ result:type_alias_declaration { result.export = true; return result; }
     / ambient_variable_declaration
     / ambient_function_declaration
     / ambient_class_declaration
     / interface_declaration
     / ambient_enum_declaration
     / ambient_module_declaration
     / import_declaration
+    / type_alias_declaration
     / __
 
 /* Class */