- more LDLM refcount locking infrastructure

- fixed the error handling paths of unlink and rmdir, so that unlinking a
non-existant file returns an error
- fixed the DLM bug that caused the perl script to hang (there's a new bug now
  that it triggers under heavier load that causes it to crash)
- fixed a second crashing bug that occurred if a blocked lock gets completed
  and then cancelled all before the server-side enqueue finishes (amazing but
  true)
- osc_open() now returns the actual rc instead of 0
- fixed a race condition in ptlrpc/service.c related to thread shutdown (nice
  catch, Mike)