Miscellany.

- make the printk in buffer_io_error() sector_t-aware.

- Some buffer.c cleanups from AntonA: remove a couple of !uptodate
  checks, and set a new buffer's b_blocknr to -1 in a more sensible
  place.

- Make buffer_head.b_size a 32-bit quantity.  Needed for 64k pagesize
  on ia64.  Does not increase sizeof(struct buffer_head).