make "card type" unique per device (Closes: #37)

some broken applications will only allow you to select the first device of
a given "card type".
in order to make all loopback devices selectable, we encode the device
number into the card type.
"Dummy video device" becomes (e.g.) "Dummy video device (0x003)"
always provide format-string when using printf()

even if it's only "%s".