def get_constant
      res = ""
      skip_tkspace(false)
      tk = get_tk

      while tk.kind_of?(TkCOLON2) ||
          tk.kind_of?(TkCOLON3)   ||
          tk.kind_of?(TkCONSTANT)          
        
        res += tk.text
        tk = get_tk
      end

#      if res.empty?
#        warn("Unexpected token #{tk} in constant")
#      end 
      unget_tk(tk)
      res
    end
def get_constant
      res = ""
      skip_tkspace(false)
      tk = get_tk

      while tk.kind_of?(TkCOLON2) ||
          tk.kind_of?(TkCOLON3)   ||
          tk.kind_of?(TkCONSTANT)          
        
        res += tk.text
        tk = get_tk
      end

#      if res.empty?
#        warn("Unexpected token #{tk} in constant")
#      end 
      unget_tk(tk)
      res
    end
Parse a constant, which might be qualified by
 one or more class or module names