ROOM_S_DARK_MSG		Replaces the old 'It is too dark to' fail
			message with a customizable string. Note
                        that the action verb is appended to this string
			when printed out. If this property is not
			defined, the old 'It is too dark to' message
			will be used instead.
			Example:
			add_prop(ROOM_S_DARK_MSG,
				"The fog is too thick here to");

                        This will output something like:
                        'The fog is too thick here to see.' when the
                        player does a look.
