warnings fix

slap_send_ldap_result() when rs->sr_flags & REP_REF_MUSTBEFREED:
- Do not return with rs->sr_ref == <freed data>, set it to NULL instead.
- Plug memory leak when op->o_domain_scope || op->o_protocol<LDAP_VERSION3.
send_ldap_response():
- Paranoia: Reset REP_MATCHED_MUSTBEFREED and REP_REF_MUSTBEFREED,
  in case the caller reuses the SlapReply without resetting the flags.

Use ldap_pvt_thread_pool_pausing(): pause check for slapd without locking.

requested. (It doesn't actually make sense to request them in that
case, but allow it.)

Unifdef SLAP_LIGHTWEIGHT_DISPATCHER
Use thread-specific data in pool_context()
Added native thread-specific data support
Concurrency tweaks:
  store conn->c_sd, don't use ber_sockbuf_ctrl to retrieve it.
  use per-thread free lists for operations, no mutexes needed.

  store conn->c_sd, don't use ber_sockbuf_ctrl to retrieve it.
  use per-thread free lists for operations, no mutexes needed.

this number tunable.)