- Convert version to flags -- a few days earlier than I said, but I'll back it

- Convert version to flags -- a few days earlier than I said, but I'll back it
  out if people complain.
- Add some helpers for accessing the lower (general) and upper (op-specific)
  portions of the flags.
- Use an op flag (MDS_OPEN_HAS_EA) rather than bufcount checking to determine
  whether or not an open has an EA for delayed-create.
- Remove basically-unused rq_reply_md_h.
- Pack open-replay state in extra message buffer, instead of dangling it off the
  request.
- Add DEBUG_REQ for consistent and clean request-dumping, and use it somewhat
  liberally.
- Teach reint_link to be tolerant of -EEXIST if replaying.
- Likewise for reint_unlink and -ENOENT.
- Remove connection locking from ptlrpc_check_reply.  We don't lock in
  queue_wait, so if it's needed I need a better story anyway, and in the interim
  this will fix a guaranteed deadlock in replay.
- Factor sending-queue request disposition checks for legibility and reuse.
- Dump retained-request state before starting replay, to aid debugging.