firmware files for the prism2_usb kernel driver

 prism2-usb-firmware-installer will at the time of its own installation
 download the firmware files for the prism2_usb devices from the
 upstream code repository and convert them to the format used by the
 kernel modules since 2.6.32.
 .
 Note that only some adapters really need a firmware file and that
 firmware files are not completely free (in the sense of freely
 redistributable), which is why this package exists.