Function:   d2bin()

               In addition to Clipper's l2bin() and alike functions,
               d2Bin() and Bin2d() convert a Clipper Double number into a
               8 bytes long binary character. Added to Expand because d2bin()
               was needed by the 1-2-3 routines, and bin2d() was also added as
               the natural complement of it.

   Syntax:     d2Bin(<Numeric>)

   Arguments:  The Numeric expression is converted to a binary
               double precision number (std 8 bytes format).

   Returns:    An 8 bytes string, containing the binary number.