pgsql: Further code review for range types patch.

Further code review for range types patch.

Fix some bugs in coercion logic and pg_dump; more comment cleanup;
minor cosmetic improvements.

Branch
------
master

Details
-------
http://git.postgresql.org/pg/commitdiff/b985d48779146b7ba969b0963614ad7683589bc8

Modified Files
--------------
doc/src/sgml/datatype.sgml | 22 ++--
src/backend/catalog/pg_proc.c | 47 +++++----
src/backend/commands/typecmds.c | 11 +-
src/backend/parser/parse_coerce.c | 196 +++++++++++++++++++---------------
src/backend/tcop/utility.c | 4 +-
src/backend/utils/cache/lsyscache.c | 10 ++-
src/backend/utils/cache/syscache.c | 4 +-
src/backend/utils/fmgr/funcapi.c | 67 ++++++------
src/bin/pg_dump/pg_dump.c | 145 ++++++++++---------------
src/include/nodes/parsenodes.h | 20 ++--
src/include/utils/builtins.h | 2 +
src/include/utils/rangetypes.h | 4 +-
src/pl/plpgsql/src/pl_comp.c | 8 +-
13 files changed, 275 insertions(+), 265 deletions(-)