pgsql: In pg_upgrade, track only one copy of namespace/relname in FileN

In pg_upgrade, track only one copy of namespace/relname in FileNameMap
because the old and new values are identical.

Branch
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master

Details
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http://git.postgresql.org/gitweb?p=postgresql.git;a=commitdiff;h=f75383e6e8263cd98582edb0b3884132ad9e368a

Modified Files
--------------
contrib/pg_upgrade/info.c | 17 +++++++----------
contrib/pg_upgrade/pg_upgrade.h | 7 ++-----
contrib/pg_upgrade/relfilenode.c | 24 +++++++++---------------
3 files changed, 18 insertions(+), 30 deletions(-)