First C Device API Draft

Hi,

I tried to commit my first draft for the low level device API --
unfortunately ssh doesn't work any longer on my machine and therefore I had to zip what
I've done (http://cs.tu-berlin.de/~bonefish/download/partscan.zip). In
absence of an idea for a better name, the kernel module bundling the functionality
for getting information about sessions and partitions of devices is called
partscan (for partition scanner, better suggestions are welcome :-) and resides
in `src/add-ons/kernel/partscan'. The modules for sessions, partitions and
FSs go into the respective subdirs. Currently only one, `partition/intel',
being able to recognize DOS partition maps is implemented.

The headers for the modules live in `headers/private/partscan'. They contain
a bit of documentation about there API. The user API is defined in
`headers/os/kernel/fs_device.h'.

In `src/tests/add-ons/kernel/partscan' the user land versions of the modules
are built and there's also some test code.

As said, this is a first draft. Suggestions/ideas are very welcome.

CU, Ingo