pgsql: Revert the default toast compression strategy to the former

Log Message:
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Revert the default toast compression strategy to the former behavior
where there's no limit on the size of datum we'll try to compress.
Other 8.4 tweaks to the behavior remain in place.  Per discussion.

Modified Files:
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    pgsql/src/backend/utils/adt:
        pg_lzcompress.c (r1.32 -> r1.33)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/adt/pg_lzcompress.c?r1=1.32&r2=1.33)