Optimize SD card partitioning and formatting for SD/Flash

This implements the recommendations to optimize the SDCard/Flash partitioning and formatting.
Also, it drops the dependency on `parted`, which is nice, imho.

Note that the parameters are default values which are proven to work best on most SD card. You could grab more optim by having per-sd parameters (erase blocks, for instance). But 4mb will get us pretty far by itself and will work on most sd cards.

I'm seeing noticeable performance increase when writing the SD (+50% throughput on small random writes).

More info at:

- http://blogofterje.wordpress.com/2012/01/14/optimizing-fs-on-sd-card/
- http://www.raspberrypi.org/phpBB3/viewtopic.php?f=9&t=850
- http://forum.xda-developers.com/showthread.php?t=1224408