Allow user to use $this to refer to page class in page markup file.

example:
<html>
	<body>
	<?php 
		$this->TextBox1->Text();
	?>
	<php:TextBox1 runat="server" ID="TextBox1" />
	</body>
</html>

Change-Id: Ifabef73fca1816a00775920ba9448baa62d8a584