Fix Source.info to correctly print header comments

        excluded_cards = {'SIMPLE', 'BITPIX', 'NAXIS', 'EXTEND', 'DATE',

                          'AUTHOR'}

        for key in self.header.keys():

            if key not in excluded_cards:

                info(self.header.cards[key])

        for card in self.header.cards:

            if card.keyword not in excluded_cards:

                info(card)

        for attr in (self.spectra, self.images, self.cubes, self.tables):

            info(repr(attr))