CGA40()
 Switches to 40-column mode (color or monochrome)
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 Syntax

     CGA40([<lMonochromeMode>]) --> lSwitch

 Argument

     <lMonochromeMode>  Designates the 40.character mode.  If this
     parameter is .T., the function switches to the monochrome CGA
     40-character mode.  If this parameter is.F., the function switches to
     the 40-character color mode.  The default value is .F..

 Returns

     CGA40() returns .T. if the screen adapter you use permits a switch.

 Description

     This function can be used with any screen adapter that has CGA emulation
     capability.  You can switch to CGA 40-character mode, color or
     monochrome.  The function ISCOLOR() also returns .T. in the monochrome
     mode because this option activates a "color summing" of the screen
     adapter and does not switch to the monochrome mode for a hercules
     adapter or a monochrome text adapter.

 Notes

     Important!  This function cannot be implemented when windows are
     open.

     .  Modes set through this function can also be combined with
        other line counts, i.e. EGA43().

     .  A call with .T. corresponds to BIOS mode 0.  A call with .F.
        corresponds to BIOS mode 1.

 Examples

     .  Switch to 40-character mode (color):

        ?  CGA40()         //  .T., if successful

     .  Switch to 40-character mode (monochrome):

        ?  CGA40(.T.)      //  .T., if successful