[js] use js.RegExp instead of Dynamic in EReg

std/js/_std/EReg.hx

@@ -21,11 +21,11 @@
  */
 @:coreApi class EReg {
 
-	var r : Dynamic;
+	var r : HaxeRegExp;
 
 	public function new( r : String, opt : String ) : Void {
 		opt = opt.split("u").join(""); // 'u' (utf8) depends on page encoding
-		this.r = untyped __new__("RegExp",r,opt);
+		this.r = new HaxeRegExp(r, opt);
 	}
 
 	public function match( s : String ) : Bool {
@@ -110,3 +110,9 @@
 		return buf.toString();
 	}
 }
+
+@:native("RegExp")
+private extern class HaxeRegExp extends js.RegExp {
+	var m:js.RegExp.RegExpMatch;
+	var s:String;
+}