pgsql: Use ResultRelInfo ** rather than ResultRelInfo * for tuple routi

Use ResultRelInfo ** rather than ResultRelInfo * for tuple routing.

The previous convention doesn't lend itself to creating ResultRelInfos
lazily, as we already do in ExecGetTriggerResultRel. This patch
doesn't make anything lazier than before, but the pending patch for
UPDATE tuple routing proposes to do so (and there might be other
opportunities as well).

Amit Khandekar with some adjustments by me.

Discussion: http://postgr.es/m/CA+TgmoYPVP9Lyf6vUFA5DwxS4c--x6LOj2y36BsJaYtp62eXPQ@mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/60f7c0abef0327648c02795312d1679c66586fbb

Modified Files
--------------
src/backend/commands/copy.c | 10 ++---
src/backend/executor/execMain.c | 13 +++---
src/backend/executor/nodeModifyTable.c | 74 ++++++++++++++++++++--------------
src/include/executor/executor.h | 2 +-
src/include/nodes/execnodes.h | 2 +-
5 files changed, 57 insertions(+), 44 deletions(-)