pgsql: Fix PlanRowMark/ExecRowMark structures to handle inheritance cor

Fix PlanRowMark/ExecRowMark structures to handle inheritance correctly.

In an inherited UPDATE/DELETE, each target table has its own subplan,
because it might have a column set different from other targets. This
means that the resjunk columns we add to support EvalPlanQual might be
at different physical column numbers in each subplan. The EvalPlanQual
rewrite I did for 9.0 failed to account for this, resulting in possible
misbehavior or even crashes during concurrent updates to the same row,
as seen in a recent report from Gordon Shannon. Revise the data structure
so that we track resjunk column numbers separately for each subplan.

I also chose to move responsibility for identifying the physical column
numbers back to executor startup, instead of assuming that numbers derived
during preprocess_targetlist would stay valid throughout subsequent
massaging of the plan. That's a bit slower, so we might want to consider
undoing it someday; but it would complicate the patch considerably and
didn't seem justifiable in a bug fix that has to be back-patched to 9.0.

Branch
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REL9_0_STABLE

Details
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http://git.postgresql.org/gitweb?p=postgresql.git;a=commitdiff;h=fed8dcdb84d255088d22efa3156a193f3399e792

Modified Files
--------------
src/backend/executor/execJunk.c | 14 ++++-
src/backend/executor/execMain.c | 107 ++++++++++++++++++++++++--------
src/backend/executor/nodeLockRows.c | 51 ++++++++--------
src/backend/executor/nodeModifyTable.c | 42 +++++++------
src/backend/nodes/copyfuncs.c | 3 -
src/backend/nodes/outfuncs.c | 3 -
src/backend/optimizer/plan/planner.c | 8 ---
src/backend/optimizer/prep/preptlist.c | 17 +-----
src/backend/optimizer/prep/prepunion.c | 4 -
src/include/executor/executor.h | 10 ++-
src/include/nodes/execnodes.h | 34 ++++++++---
src/include/nodes/plannodes.h | 21 +++++--
12 files changed, 192 insertions(+), 122 deletions(-)