pgsql-server: Still another try at automatically detecting the best

Log Message:
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Still another try at automatically detecting the best match in the zic
timezone database for the system behavior we find ourselves in.  Scan
backwards from current time and choose the zone that matches furthest
back.  As per discussion a week or so back.

Modified Files:
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    pgsql-server/src/timezone:
        pgtz.c (r1.18 -> r1.19)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql-server/src/timezone/pgtz.c.diff?r1=1.18&r2=1.19)