dosfstools updates

dosfstools 2.8vb2 source, or patch against 2.8
From ChangeLog:

 - mkdosfs: Print usage message if no device specified, fix s390
   from RedHat.
 - mkdosfs: Automatically select FAT32 and cluster size based on
   Microsoft criteria.
 - modosfs: Added low memory mode (-M).
 - dosfsck: Fix for FAT32 on 64 bit platforms, check end of filesystem 
   from Richard Hirst .
 - dosfsck: Clean up exit values.
 - dosfsck: Add low memory mode (-m).