* bus/config-parser.c (struct BusConfigParser): Added
	    included_files field.
	    (seen_include): Added.  Checks whether or not a file has already
	    been included by any parent BusConfigParser.
	    (bus_config_parser_new): Copy the parent's included_files.
	    (include_file): Track which files have been included, and fail on
	    circular inclusions.
	    (process_test_valid_subdir): Changed printf to report if we are
	    testing valid or invalid conf files.
	    (all_are_equiv): Changed printf to be a bit clearer about
	    what we are actually doing.
	    (bus_config_parser_test): Test invalid configuration files.