pgsql: Add a relkind field to RangeTblEntry to avoid some syscache look

Add a relkind field to RangeTblEntry to avoid some syscache lookups.

The recent additions for FDW support required checking foreign-table-ness
in several places in the parse/plan chain.  While it's not clear whether
that would really result in a noticeable slowdown, it seems best to avoid
any performance risk by keeping a copy of the relation's relkind in
RangeTblEntry.  That might have some other uses later, anyway.
Per discussion.

Branch
------
master

Details
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http://git.postgresql.org/pg/commitdiff/bdca82f44d0e0168dece56cbd53b54ba142f328f

Modified Files
--------------
src/backend/catalog/dependency.c      |    1 +
src/backend/commands/copy.c           |    1 +
src/backend/nodes/copyfuncs.c         |    1 +
src/backend/nodes/equalfuncs.c        |    1 +
src/backend/nodes/nodeFuncs.c         |    2 -
src/backend/nodes/outfuncs.c          |    2 +-
src/backend/nodes/print.c             |    8 +---
src/backend/nodes/readfuncs.c         |    2 +-
src/backend/optimizer/path/allpaths.c |   67 +++++++++++++++++----------------
src/backend/optimizer/plan/planner.c  |    3 +-
src/backend/parser/analyze.c          |   23 +++--------
src/backend/parser/parse_relation.c   |    2 +
src/backend/parser/parse_target.c     |    2 -
src/backend/rewrite/rewriteHandler.c  |    9 ++++-
src/backend/utils/adt/ri_triggers.c   |    2 +
src/backend/utils/adt/ruleutils.c     |    7 +++-
src/include/catalog/catversion.h      |    2 +-
src/include/catalog/pg_class.h        |   17 ++++----
src/include/nodes/parsenodes.h        |    7 ++-
19 files changed, 85 insertions(+), 74 deletions(-)