* dbus/dbus-sysdeps.c (_dbus_file_get_contents): include filenames
	in error messages
	(_dbus_string_get_dirname): new
	(_dbus_sysdeps_test): new
	(_dbus_directory_open): include dirnames in error messages

	* bus/config-parser.c: interpret <include> and <includedir> and
	<servicedir> relative to config file location if the given
	filename is not absolute.

	* dbus/dbus-string.c (_dbus_string_find_byte_backward): new