Обсуждение: pgsql: Fix LIMIT/OFFSET for null limit values.

Log Message:
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Fix LIMIT/OFFSET for null limit values.  This worked before 8.2 but was broken
by the change to make limit values int8 instead of int4.  (Specifically, you
can do DatumGetInt32 safely on a null value, but not DatumGetInt64.)  Per
bug #2803 from Greg Johnson.

Modified Files:
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    pgsql/src/backend/executor:
        nodeLimit.c (r1.27 -> r1.28)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/executor/nodeLimit.c.diff?r1=1.27&r2=1.28)