in progress:  raw (low level) ISRC reads

**do not merge yet** (this is for progress tracking again)

Most of the implementation for raw reading of CDs to get the Q sub-channels and the ISRCs in them is platform independent.
The only thing that is platform specific is `scsi_cmd` to issue a direct scsi command.

Raw reads are only optional in the spec (so I would keep other options as backup solution) and we might need to test for the support somehow.
Additionally: virtually all programs use the (more high level) "sub-channel command" approach. So that approach is tested and our "raw approch" would need more testing.

We also have to test and probably fix building again since we use new files and have new internal dependencies.

First tests show, that raw reading really fixes [LIB-11](http://tickets.musicbrainz.org/browse/LIB-11)

*note*: This is is forked off `isrc_raw`, but that will soon go into master. Only the last commit is about raw reads (as of Feb 4th).