pgsql: Cleanup of rewriter and planner handling of Query.hasRowSecurity

Cleanup of rewriter and planner handling of Query.hasRowSecurity flag.

Be sure to pull up the subquery's hasRowSecurity flag when flattening a
subquery in pull_up_simple_subquery().  This isn't a bug today because
we don't look at the hasRowSecurity flag during planning, but it could
easily be a bug tomorrow.

Likewise, make rewriteRuleAction() pull up the hasRowSecurity flag when
absorbing RTEs from a rule action.  This isn't a bug either, for the
opposite reason: the flag should never be set yet.  But again, it seems
like good future proofing.

Add a comment explaining why rewriteTargetView() should *not* set
hasRowSecurity when adding stuff to securityQuals.

Improve some nearby comments about securityQuals processing, and document
that field more completely in parsenodes.h.

Patch by me, analysis by Dean Rasheed.

Discussion: <CAEZATCXZ8tb2DV6f=bkhsMV6u_gRcZ0CZBw2J-qU84RxSukZog@mail.gmail.com>

Branch
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master

Details
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http://git.postgresql.org/pg/commitdiff/24aef33804be5d7d71bc3932ced3407fce71e354

Modified Files
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src/backend/optimizer/prep/prepjointree.c |  3 +++
src/backend/rewrite/rewriteHandler.c      | 32 ++++++++++++++++++++++++-------
src/include/nodes/parsenodes.h            |  9 ++++++++-
3 files changed, 36 insertions(+), 8 deletions(-)