XPgetText()
  Get text from a screen position.
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   Function:   XPgetText()

               XPgetText() retrieves text from a screen position and returns
               it in a string variable.

   Syntax:     XPgetText(nRow,nCol,nLen) --> cText

   Arguments:  <nRow>,<nCol> is the position on the screen where to
               fetch the text. <nLen> is the length of the text to fetch.

   Returns:    a String, which is what is on the screen at that time.

   Usage:      /* Get last screen line */
               Text := XPgetText(MaxRow(),0,MaxCol()+1)