doc/obd-howto.sgml: updated for initial public release

obdfs/many: changed to have separate dir/file operations,
ext2obd/ext2_obd.c:  cosmetic changes to match ext2 code more closely (for diff)
include/linux/obd_class.h: change obdo_{cpy,cmp}_md() to allow
  include or exclude flags for copy/compare of metadata
snap/snaptable.c: comment iterator functions clearly