pgsql: Accept "+infinity" in date and timestamp[tz] input.

Accept "+infinity" in date and timestamp[tz] input.

The float and numeric types accept this variant spelling of
"infinity", so it seems like the datetime types should too.

Vik Fearing, some cosmetic mods by me

Discussion: https://postgr.es/m/d0bef637-2dbd-0a5d-e539-48243b6f6c5e@postgresfriends.org

Branch
------
master

Details
-------
https://git.postgresql.org/pg/commitdiff/2ceea5adb02603ef52579b568ca2c5aebed87358

Modified Files
--------------
src/backend/utils/adt/datetime.c | 1 +
src/test/regress/expected/date.out | 6 ++++++
src/test/regress/expected/timestamp.out | 6 ++++++
src/test/regress/expected/timestamptz.out | 6 ++++++
src/test/regress/sql/date.sql | 2 ++
src/test/regress/sql/timestamp.sql | 2 ++
src/test/regress/sql/timestamptz.sql | 2 ++
7 files changed, 25 insertions(+)