pgsql: Account for SRFs in targetlists in planner rowcount estimates.

Account for SRFs in targetlists in planner rowcount estimates.

We made use of the ROWS estimate for set-returning functions used in FROM,
but not for those used in SELECT targetlists; which is a bit of an
oversight considering there are common usages that require the latter
approach.  Improve that.  (I had initially thought it might be worth
folding this into cost_qual_eval, but after investigation concluded that
that wouldn't be very helpful, so just do it separately.)  Per complaint
from David Johnston.

Back-patch to 9.2, but not further, for fear of destabilizing plan choices
in existing releases.

Branch
------
master

Details
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http://git.postgresql.org/pg/commitdiff/31c7c642b6419b43eff903285e3da65e3f1901d6

Modified Files
--------------
src/backend/optimizer/path/costsize.c   |    9 +++-
src/backend/optimizer/plan/createplan.c |   29 ++++--------
src/backend/optimizer/plan/planagg.c    |    6 +--
src/backend/optimizer/plan/planner.c    |   78 ++++++++++++++++++++++--------
src/backend/optimizer/util/clauses.c    |   42 +++++++++++++++-
src/include/optimizer/clauses.h         |    1 +
src/include/optimizer/planner.h         |    3 +
7 files changed, 120 insertions(+), 48 deletions(-)