* configure.in: add --enable-checks

	* dbus/dbus-message.c (dbus_message_new): reverse name/service arguments

	* dbus/dbus-connection.c (dbus_connection_preallocate_send): fix
	to use thread locks.
	(_dbus_connection_handler_destroyed_locked): move some private
	functions into proper docs group

	* dbus/dbus-internals.h: add _dbus_return_if_fail,
	_dbus_return_val_if_fail

	Throughout: use dbus_return_if_fail