ecma262-compatible named func expr

Changed the scope of names of function expressions to follow ecma-262.
```
class _Main {
	static function main(args : string[]) : void {
		function f () : void {
			f;	// ok
		}

		var _ = function g () : void {
			g;	// ok
		};

		f;  // ok
		g; // ng
	}
}
```