Silence -Wunused-result warning in contrib/pg_upgrade.

This is just neatnik-ism, but since we do it for comparable code in elog.c,
we may as well do it here.

Branch
------
REL9_2_STABLE

Details
-------
http://git.postgresql.org/pg/commitdiff/970212f911728097b44ac231438c5cf4d45b2089

Modified Files
--------------
contrib/pg_upgrade/util.c |   12 ++++++++++--
1 files changed, 10 insertions(+), 2 deletions(-)

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