Add support for accessing individual tracks on a CD.

Add support for accessing individual tracks on a CD.

This is done by misusing the device minor a bit to encode the
track no there.

So to read track #4 just use /dev/acdNt4 where N is the device #.

The driver no automatically sets the blocksize (sectorsize) to
what the track is set to in the TOC.

This has the nice effect that you can now rip audioi tracks
by simply doing:

dd if=/dev/acdNt2 of=audiotrack2.raw bs=2352

it cant be much simpler than that :)

NOTE: the original acdNa & acdNc device still work as usual,
except the blocksize is set according to track0.