* as.c (show_usage): Add -am.

    * as.c (show_usage): Add -am.
        * input-scrub.c (input_scrub_include_sb): Don't add leading \n
        if we've already got one.
        * listing.c (struct list_info_struct): Add line_contents.
        (listing_newline): Put unused argument to work: if non-null, save it...
        (listing_listing): ... and regurgitate during listing instead of line
        from file.
        * listing.h (LISTING_MACEXP): New define.
        (LISTING_NEWLINE): Argument is NULL.
        * read.c (read_a_source_file): If expanding macros, break up input
        lines and pass them to listing_newline.
        * doc/as.texinfo: Document -ac and -am.

        * cond.c (s_ifc): Add missing demand_empty_rest_of_line.