* dbus/dbus-message-factory.c (generate_special): more test cases,
	increasing coverage

	* dbus/dbus-marshal-validate.c (validate_body_helper): return the
	reason why a signature was invalid

	* dbus/dbus-marshal-header.c (load_and_validate_field): fix to
	skip the length of the string before we look at it in validation

	* dbus/dbus-string-util.c (_dbus_string_test): add tests for
	equal_substring

	* dbus/dbus-message.c (_dbus_message_loader_new): default
	max_message_length to DBUS_MAXIMUM_MESSAGE_LENGTH