* bus/bus.c (process_config_every_time): Drop existing conf-dir
        watches (if applicable) and add new watches

        * bus/main.c (signal_handler): Handle SIGIO if using D_NOTIFY
        (main): Setup SIGIO signal handler if using D_NOTIFY

        * bus/config-parser.h: Add prototype bus_config_parser_get_conf_dirs

        * bus/config-parser.c (struct BusConfigParser): Add conf_dirs list
        (merge_included): Also merge conf_dirs list
        (bus_config_parser_unref): Clear conf_dirs list
        (include_dir): Add directory to conf_dirs list
        (bus_config_parser_get_conf_dirs): New function

        * bus/dir-watch.[ch]: New files

        * bus/Makefile.am (BUS_SOURCES): Add dir-watch.[ch]

        * configure.in: Add checks for D_NOTIFY on Linux