pgsql: Fix "element <@ range" cost estimation.

Fix "element <@ range" cost estimation.

The statistics-based cost estimation patch for range types broke that, by
incorrectly assuming that the left operand of all range oeprators is a
range. That lead to a "type x is not a range type" error. Because it took so
long for anyone to notice, add a regression test for that case.

We still don't do proper statistics-based cost estimation for that, so you
just get a default constant estimate. We should look into implementing that,
but this patch at least fixes the regression.

Spotted by Tom Lane, when testing query from Josh Berkus.

Branch
------
master

Details
-------
http://git.postgresql.org/pg/commitdiff/f897c4744fea221dfc7bbd277081edad41d1d58d

Modified Files
--------------
src/backend/utils/adt/rangetypes_selfuncs.c |    6 ++++--
src/test/regress/expected/rangetypes.out    |   11 +++++++++++
src/test/regress/sql/rangetypes.sql         |    9 +++++++++
3 files changed, 24 insertions(+), 2 deletions(-)