pgsql: Remove the nexus between trial_buffs and trial_conns, and don't

Log Message:
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Remove the nexus between trial_buffs and trial_conns, and don't test shared buffers lower than or equal to a value we
alreadyknow is good, but use that value instead. This will make it easier to adjust the trial values and/or formulae in
futureif necessary. 

Modified Files:
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    pgsql/src/bin/initdb:
        initdb.c (r1.103 -> r1.104)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/bin/initdb/initdb.c.diff?r1=1.103&r2=1.104)