pgsql: Remove PlannerInfo's join_search_private method.

Remove PlannerInfo's join_search_private method.

Instead, use the new mechanism that allows planner extensions to store
private state inside a PlannerInfo, treating GEQO as an in-core planner
extension. This is a useful test of the new facility, and also buys
back a few bytes of storage.

To make this work, we must remove innerrel_is_unique_ext's hack of
testing whether join_search_private is set as a proxy for whether
the join search might be retried. Add a flag that extensions can
use to explicitly signal their intentions instead.

Reviewed-by: Andrei Lepikhov <lepihov(at)gmail(dot)com>
Reviewed-by: Melanie Plageman <melanieplageman(at)gmail(dot)com>
Reviewed-by: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Discussion: http://postgr.es/m/CA+TgmoYWKHU2hKr62Toyzh-kTDEnMDeLw7gkOOnjL-TnOUq0kQ@mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/64095d157482136ee609586266f8a37467c69bde

Modified Files
--------------
src/backend/optimizer/geqo/geqo_eval.c | 2 +-
src/backend/optimizer/geqo/geqo_main.c | 12 ++++++++++--
src/backend/optimizer/geqo/geqo_random.c | 7 +++----
src/backend/optimizer/plan/analyzejoins.c | 9 +++------
src/backend/optimizer/plan/planner.c | 1 +
src/backend/optimizer/prep/prepjointree.c | 1 +
src/include/nodes/pathnodes.h | 5 ++---
src/include/optimizer/geqo.h | 12 +++++++++++-
8 files changed, 32 insertions(+), 17 deletions(-)