- Do the LOCK_CHANGED work in ldlm_lock_enqueue inside an ns_lock; it was making

- Do the LOCK_CHANGED work in ldlm_lock_enqueue inside an ns_lock; it was making
  me nervous without.
- The lock may have already received a blocking AST, while it was still owned
  by the server.  In this case, the client will receive the lock, oblivious to
  the fact that it needs to be given up.  Unset the "AST already sent" flag
  before handing the lock to the client.
- Add mdc_sem calls around ldlm_cli_enqueue in mdc_request