pgsql: Reject combining "epoch" and "infinity" with other datetime fiel

Reject combining "epoch" and "infinity" with other datetime fields.

Datetime input formerly accepted combinations such as
'1995-08-06 infinity', but this seems like a clear error.
Reject any combination of regular y/m/d/h/m/s fields with
these special tokens.

Joseph Koshakow, reviewed by Keisuke Kuroda and myself

Discussion: /messages/by-id/CAAvxfHdm8wwXwG_FFRaJ1nTHiMWb7YXS2YKCzCt8Q0a2ZoMcHg@mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/bcc704b52490492e6bd73c4444056b3e9644504d

Modified Files
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src/backend/utils/adt/datetime.c | 40 ++++++++++------
src/test/regress/expected/horology.out | 85 ++++++++++++++++++++++++++++++++++
src/test/regress/sql/horology.sql | 23 +++++++++
3 files changed, 133 insertions(+), 15 deletions(-)