* dbus/dbus-bus.c: add more return_if_fail checks

	* dbus/dbus-message.c (load_message): have the "no validation"
	mode (have to edit the code to toggle the mode for now though)

	* dbus/dbus-marshal-header.c (_dbus_header_load): have a mode that
	skips all validation; I want to use this at least for benchmark
	baseline, I'm not sure if it should be a publicly-available switch.