[Laszlo-dev] Bug: Chapter 28. Classes

[P T Withington]

This section needs to be updated to use the `lz.` namespace in the  
examples.  Needs to say `new lz.PopupWindow`.

[Chapter 28. Classes](http://www.openlaszlo.org/lps4.1/docs/developers/introductory-classes.html#d0e71025 
)