pgsql: Fix wrong WAL info value generated when gistContinueInsert()

Log Message:
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Fix wrong WAL info value generated when gistContinueInsert() performs an
index page split.  This would result in index corruption, or even more likely
an error during WAL replay, if we were unlucky enough to crash during
end-of-recovery cleanup after having completed an incomplete GIST insertion.

Yoichi Hirai

Tags:
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REL8_3_STABLE

Modified Files:
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    pgsql/src/backend/access/gist:
        gistxlog.c (r1.27 -> r1.27.2.1)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/access/gist/gistxlog.c?r1=1.27&r2=1.27.2.1)