MDIWindow inappropriately sets size constraints in constructor

[nekenyu]

MDIWindow.MDIWindow() contains the undocumented "feature": minWidth = minHeight = width = height = 200;

This class only knows that it contains a title bar. Setting any other size constraints is pure speculation which confounds automatic layout and requires an undocumented hack from mx.Panel to set these values to NaN to (mostly?) work around..