Thread redesign

The following patch creates a separate configuration variable for each
function requiring thread safety. This allows better selection of *_r
function names. It also removes thread locking around non-thread-safe
function because the application could call those from its own code.

Platforms will have to re-run tools/thread to report their thread-safe
functions.

-- 
  Bruce Momjian                        |  http://candle.pha.pa.us
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