pgsql: Still more review for range-types patch.

Still more review for range-types patch.

Per discussion, relax the range input/construction rules so that the
only hard error is lower bound > upper bound. Cases where the lower
bound is <= upper bound, but the range nonetheless normalizes to empty,
are now permitted.

Fix core dump in range_adjacent when bounds are infinite. Marginal
cleanup of regression test cases, some more code commenting.

Branch
------
master

Details
-------
http://git.postgresql.org/pg/commitdiff/766948beddef66dd89563f465919eca6e131861c

Modified Files
--------------
src/backend/utils/adt/rangetypes.c | 472 ++++++++++++++++++------------
src/backend/utils/adt/rangetypes_gist.c | 45 ++--
src/include/utils/rangetypes.h | 5 +
src/test/regress/expected/rangetypes.out | 309 ++++++++++++--------
src/test/regress/sql/rangetypes.sql | 97 ++++---
5 files changed, 556 insertions(+), 372 deletions(-)