pgsql: Re-allow input of Julian dates prior to 0001-01-01 AD.

Re-allow input of Julian dates prior to 0001-01-01 AD.

This was unintentionally broken in 8.4 while tightening up checking of
ordinary non-Julian date inputs to forbid references to "year zero".
Per bug #5672 from Benjamin Gigot.

Branch
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master

Details
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http://git.postgresql.org/gitweb?p=postgresql.git;a=commitdiff;h=9aae81527f3174b9b6fd6366f04435310903dab2

Modified Files
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src/backend/utils/adt/datetime.c | 37 +++++++++++++++++++++----------
src/test/regress/expected/horology.out | 13 +++++++++++
src/test/regress/sql/horology.sql | 3 ++
3 files changed, 41 insertions(+), 12 deletions(-)