Improve pg_hba.conf

I think there should be a way to specify usernames directly in
pg_hba.conf. We do have the secondary password files, but puting the
usernames right in the file should be possible. I will put it on the
TODO list and discuss it later for 7.3.

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