warnings fix

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.

Note: this breaks LDAP_COMP_MATCH and SLAP_ZONE_MALLOC. But they
were probably broken already anyway.

allow comma-separated descriptive log levels, so that tests can be run, e.g., with "SLAPD_DEBUG=stats,stats2"; s/ldap_debug/slap_debug/

unintentional changed default of TLSVerifyClient.