Class UpWindow:
~~~~~~~~~~~~~~~
The same as the class Window, but due to redefining of instvar variable
UpWindow:UpfFlag to the default value true it is not possible to deactivate
this window and to switch to other. It will remain on the top of the stack
of windows.

Common use:
~~~~~~~~~~~
When we need the window not to switch to background.

Source code is in C_UpWind.prg