pgsql: Check for overflow in strtol() while parsing datetime inputs.

Log Message:
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Check for overflow in strtol() while parsing datetime inputs.
Michael Fuhr.

Tags:
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REL8_1_STABLE

Modified Files:
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pgsql/src/backend/utils/adt:
datetime.c (r1.160.2.1 -> r1.160.2.2)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/adt/datetime.c.diff?r1=1.160.2.1&r2=1.160.2.2)