- Comment and documentation fixlets

- Remove some unneeded fields from swapper_inode (these are a
  leftover from when I had swap using the filesystem IO functions).

- fix a printk bug in pci/pool.c: when dma_addr_t is 64 bit it
  generates a compile warning, and will print out garbage.  Cast it to
  unsigned long long.

- Convert some writeback #defines into enums (Steven Augart)