Apply patch from Steve Sonntag <vtag@novell.com>

Copyright 2000 Stig Venaas, UNINETT
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o start it as a service (gets around an annoying pause when starting u
p as a non-service).

Misc other header changes.

r/w locks and thread pools.  Hide internal structures (using
pthread'ish technics).  Place common code in threads.c.  Move
no-thread code to thr_stub.c.  Move thread pool code to tpool.c.
Removed setconcurrency call from initializer, added 'concurrency'
directive to slapd.  Tested code under pthreads, pth, and no-threads.

 (on Linux), with max_concurrency set to 0 (as many as needed), 1, 2,
and 3.

in attempt to get it work with GNU PTH.

macros LUTIL_STRDUP and friends).

Plus more pthread rwlock code

Update comment with reference to publically available examples.