'C' Shadow routine that works with DISPBEGIN()/DISPEND()
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 Syntax

       GT_CShadow(<nTop>, <nBottom>, <nLeft>, <nRight>) --> NIL

 Arguments:

     <nTop> Top of box

     <nLeft> Left of box

     <nBottom> Bottom of box

     <nRight> Right of box

 Returns:

     NIL

 Description:

     Draws a shadow around a box area (1 character on bottom and 2 on the
     right.

     Note: The module also includes a C/ASM callable function equivelant
           in the form of:

              void gt_Shadow (int t, int l, int b, int r);

 Examples:

     @ 10, 20 TO 16, 60 DOUBLE
     GT_CShadow(10, 20, 16, 60)

 Source: SHADOW.C

 Author:  Ian 'DrDebug' Day (Dark Black Software Ltd.)