Draws a '3d(ish)' box, and opptionally labels it
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 Syntax

        GT_Block( nTop, nLeft, nBottom, nRight, ;
                  <cLabel>, <lShadow>, <cDull>, <cBright>, <cBoxChars>)

 Arguments:

      nTop,nLeft,nBottom & nRight are the coordinates
      cLabel    -   text string to be displayed *ABOVE* the box
      lShadow   -   .T./.F. for shadowing the box
      cDull     -   Darker colour pair
      cBright   -   Brighter colour pair
      cBoxChars -   Box Characters

 Returns:

      NIL

 Description:

      This routine was written to smarten up the screen display a bit.
      The idea is to try and emulate "Windows" type boxes, i.e. to draw
      them in two colours, one brighter than the other.

 Examples:



 Source: GT_BLOCK.PRG

 Author:  Simon Coates