pgsql: Add regression test to see if the min/max values of int8 convert

Log Message:
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Add regression test to see if the min/max values of int8 convert correctly.

Tags:
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REL8_1_STABLE

Modified Files:
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pgsql/src/test/regress/expected:
int8-exp-three-digits.out (r1.7 -> r1.7.2.1)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/expected/int8-exp-three-digits.out.diff?r1=1.7&r2=1.7.2.1)
int8.out (r1.10 -> r1.10.2.1)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/expected/int8.out.diff?r1=1.10&r2=1.10.2.1)
pgsql/src/test/regress/sql:
int8.sql (r1.8 -> r1.8.2.1)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/sql/int8.sql.diff?r1=1.8&r2=1.8.2.1)