Upgrade()

         Makes a progressive restore of the palette

    Syntax:

         Upgrade( cPalette ) -> Nil

         cPalette : A string of 768 bytes with the actual palette or with
                    the one wanted to be taken as reference for the upgrade.

    Description:

         This function works in synchronism with the CRT controller so that
         the degrade can offer a vision of soft and progressive change.

    Return:

         Nothing.

    Example:

         cPalette := GetPalette()
         Degrade( cPalette )
         Upgrade( cPalette )