pgsql: Get rid of the planner's LateralJoinInfo data structure.

Get rid of the planner's LateralJoinInfo data structure.

I originally modeled this data structure on SpecialJoinInfo, but after
commit acfcd45cacb6df23 that looks like a pretty poor decision.
All we really need is relid sets identifying laterally-referenced rels;
and most of the time, what we want to know about includes indirect lateral
references, a case the LateralJoinInfo data was unsuited to compute with
any efficiency. The previous commit redefined RelOptInfo.lateral_relids
as the transitive closure of lateral references, so that it easily supports
checking indirect references. For the places where we really do want just
direct references, add a new RelOptInfo field direct_lateral_relids, which
is easily set up as a copy of lateral_relids before we perform the
transitive closure calculation. Then we can just drop lateral_info_list
and LateralJoinInfo and the supporting code. This makes the planner's
handling of lateral references noticeably more efficient, and shorter too.

Such a change can't be back-patched into stable branches for fear of
breaking extensions that might be looking at the planner's data structures;
but it seems not too late to push it into 9.5, so I've done so.

Branch
------
REL9_5_STABLE

Details
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http://git.postgresql.org/pg/commitdiff/dc4518814ecc2ae319c4d1679ee079e47dbd78e9

Modified Files
--------------
src/backend/nodes/copyfuncs.c | 17 ---
src/backend/nodes/equalfuncs.c | 12 ---
src/backend/nodes/outfuncs.c | 14 +--
src/backend/optimizer/path/joinrels.c | 36 ++-----
src/backend/optimizer/plan/analyzejoins.c | 3 -
src/backend/optimizer/plan/initsplan.c | 162 ++++++++++-------------------
src/backend/optimizer/plan/planagg.c | 3 +-
src/backend/optimizer/plan/planmain.c | 6 +-
src/backend/optimizer/plan/planner.c | 3 +-
src/backend/optimizer/prep/prepjointree.c | 9 +-
src/backend/optimizer/prep/prepunion.c | 1 -
src/backend/optimizer/util/placeholder.c | 60 +++--------
src/backend/optimizer/util/relnode.c | 17 +++
src/backend/optimizer/util/var.c | 1 -
src/backend/rewrite/rewriteManip.c | 3 -
src/include/nodes/nodes.h | 1 -
src/include/nodes/relation.h | 41 +-------
17 files changed, 100 insertions(+), 289 deletions(-)