pgsql: Repair bug #2839: the various ExecReScan functions need to reset

Log Message:
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Repair bug #2839: the various ExecReScan functions need to reset
ps_TupFromTlist in plan nodes that make use of it. This was being done
correctly in join nodes and Result nodes but not in any relation-scan nodes.
Bug would lead to bogus results if a set-returning function appeared in the
targetlist of a subquery that could be rescanned after partial execution,
for example a subquery within EXISTS(). Bug has been around forever :-(
... surprising it wasn't reported before.

Tags:
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REL7_3_STABLE

Modified Files:
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pgsql/src/backend/executor:
nodeFunctionscan.c (r1.12 -> r1.12.2.1)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/executor/nodeFunctionscan.c.diff?r1=1.12&r2=1.12.2.1)
nodeIndexscan.c (r1.71 -> r1.71.2.1)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/executor/nodeIndexscan.c.diff?r1=1.71&r2=1.71.2.1)
nodeResult.c (r1.21 -> r1.21.2.1)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/executor/nodeResult.c.diff?r1=1.21&r2=1.21.2.1)
nodeSeqscan.c (r1.37 -> r1.37.2.1)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/executor/nodeSeqscan.c.diff?r1=1.37&r2=1.37.2.1)
nodeSubqueryscan.c (r1.13 -> r1.13.2.1)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/executor/nodeSubqueryscan.c.diff?r1=1.13&r2=1.13.2.1)
nodeTidscan.c (r1.26 -> r1.26.2.1)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/executor/nodeTidscan.c.diff?r1=1.26&r2=1.26.2.1)