Threading bug

I found a bug in my coding of the thread-detection logic. I was not
setting NEED_REENTRANT_FUNCS properly, so locking and *_r functions
where not being used.

The has been backpatched to 7.4.X.

-- 
  Bruce Momjian                        |  http://candle.pha.pa.us
  pgman@candle.pha.pa.us               |  (610) 359-1001
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