2004-01-06  Manish Singh  <yosh@gimp.org>

        * plug-ins/common/png.c: Implemented default settings, for both
        the UI and the PDB. Settings are stored in gimprc, but right now
        saving is broken since gimp_gimprc_set is broken right now.

        There are 3 new PDB entry points: file_png_save_defaults, which is
        a save function that only takes drawable and filename info, and
        uses the stored gimprc settings for the rest of the parameters.
        This is hooked up to the save magic, so using gimp_file_save to
        save as png now won't make big files anymore. The other two are
        file_png_get_defaults and file_png_set_defaults, which query
        and set the gimprc setting respectively.

        I also did some cleanup, and added a comment boolean to the
        file_png_save2 interface. The string serialization to the gimprc
        is sort of dumb, but it works.

        Next step is to do similar for jpeg and gif.