pgsql: Finish refactoring make_foo() functions in createplan.c.

Finish refactoring make_foo() functions in createplan.c.

This patch removes some redundant cost calculations that I left for later
cleanup in commit 3fc6e2d7f5b652b4. There's now a uniform policy that the
make_foo() convenience functions don't do any cost calculations. Most of
their callers copy costs from the source Path node, and for those that
don't, the calculation in the make_foo() function wasn't necessarily right
anyhow. (make_result() was particularly a mess, as it was serving multiple
callers using cost calcs designed for only the first one or two that had
ever existed.) Aside from saving a few cycles, this ensures that what
EXPLAIN prints matches the costs we used for planning purposes. It does
not change any planner decisions, since the decisions are already made.

Branch
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master

Details
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http://git.postgresql.org/pg/commitdiff/8c314b9853c2fbb85c041d4761426f25a9d63972

Modified Files
--------------
src/backend/optimizer/plan/createplan.c | 416 ++++++++++++++------------------
src/backend/optimizer/plan/planmain.c | 2 +-
src/backend/optimizer/plan/planner.c | 4 +-
src/backend/optimizer/util/pathnode.c | 24 +-
src/include/optimizer/pathnode.h | 4 +-
5 files changed, 201 insertions(+), 249 deletions(-)