pgsql: Un-break ecpg test suite under --disable-integer-datetimes.

Un-break ecpg test suite under --disable-integer-datetimes.

Commit 4318daecc959886d001a6e79c6ea853e8b1dfb4b broke it.  The change in
sub-second precision at extreme dates is normal.  The inconsistent
truncation vs. rounding is essentially a bug, albeit a longstanding one.
Back-patch to 8.4, like the causative commit.

Branch
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REL9_1_STABLE

Details
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http://git.postgresql.org/pg/commitdiff/019be0df10afac30b31dd28a22931602ccfba2d9

Modified Files
--------------
src/interfaces/ecpg/test/expected/pgtypeslib-dt_test2.c      |    5 +++--
src/interfaces/ecpg/test/expected/pgtypeslib-dt_test2.stdout |    1 -
src/interfaces/ecpg/test/pgtypeslib/dt_test2.pgc             |    5 +++--
3 files changed, 6 insertions(+), 5 deletions(-)