Move slock_t defines into s_lock.h

The attached applied patch moves slock_t defines into s_lock.h and moves
them out of the individual include/port files so they are centralized
and easier to maintain. This patch was already reviewed during 7.4 beta
but was recreated to match current CVS.

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