pgsql: Fix assorted oversights in range selectivity estimation.

Fix assorted oversights in range selectivity estimation.

calc_rangesel() failed outright when comparing range variables to empty
constant ranges with < or >=, as a result of missing cases in a switch.
It also produced a bogus estimate for > comparison to an empty range.

On top of that, the >= and > cases were mislabeled throughout. For
nonempty constant ranges, they managed to produce the right answers
anyway as a result of counterbalancing typos.

Also, default_range_selectivity() omitted cases for elem <@ range,
range &< range, and range &> range, so that rather dubious defaults
were applied for these operators.

In passing, rearrange the code in rangesel() so that the elem <@ range
case is handled in a less opaque fashion.

Report and patch by Emre Hasegeli, some additional work by me

Branch
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REL9_3_STABLE

Details
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http://git.postgresql.org/pg/commitdiff/527ff8baf259263cc861b2058385d92829d1ba28

Modified Files
--------------
src/backend/utils/adt/rangetypes_selfuncs.c | 50 ++++++++++++++++++---------
src/include/catalog/pg_operator.h | 4 +--
src/test/regress/expected/rangetypes.out | 32 +++++++++++++++++
src/test/regress/sql/rangetypes.sql | 4 +++
4 files changed, 72 insertions(+), 18 deletions(-)