elog patch, step 2

Here is the meat of the elog patch, phase 2. Someone complained the
previous patch was too large, so I removed the message changes to
INFO/LOG, STOP/PANIC, so you are seeing only the major changes. Of
particular interest is the GUC changes for *_min_messages. Seems to
work fine.

The next step is for me to merge the DebugLvl setting into GUC, and to
remove the DebugLvl checks from the code and have elog() do that
testing. Should I be concerned about an elog() call for every DEBUG,
even if there is no debug level set?

-- 
  Bruce Momjian                        |  http://candle.pha.pa.us
  pgman@candle.pha.pa.us               |  (610) 853-3000
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