* bus/Makefile.am:
* bus/config-parser.c: (bus_config_parser_unref),
(start_busconfig_child), (bus_config_parser_end_element),
(servicehelper_path), (bus_config_parser_content),
(bus_config_parser_finished),
(bus_config_parser_get_servicehelper),
(test_default_session_servicedirs),
(test_default_system_servicedirs), (bus_config_parser_test):
* bus/config-parser.h:
Make the config-parser code use the common config code.
Also add the session and systemdirs stuff, and make the config parser
aware of the servicehelper field.