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

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

Tags:
----
REL8_0_STABLE

Modified Files:
--------------
    pgsql/src/test/regress/expected:
        int8-exp-three-digits.out (r1.6 -> r1.6.4.1)

(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/expected/int8-exp-three-digits.out.diff?r1=1.6&r2=1.6.4.1)
        int8.out (r1.9 -> r1.9.4.1)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/expected/int8.out.diff?r1=1.9&r2=1.9.4.1)
    pgsql/src/test/regress/sql:
        int8.sql (r1.7 -> r1.7.4.1)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/sql/int8.sql.diff?r1=1.7&r2=1.7.4.1)