pgsql: pg_upgrade: don't copy/link files for invalid indexes

pg_upgrade:  don't copy/link files for invalid indexes

Now that pg_dump no longer dumps invalid indexes, per commit
683abc73dff549e94555d4020dae8d02f32ed78b, have pg_upgrade also skip
them.  Previously pg_upgrade threw an error if invalid indexes existed.

Backpatch to 9.2, 9.1, and 9.0 (where pg_upgrade was added to git)

Branch
------
REL9_0_STABLE

Details
-------
http://git.postgresql.org/pg/commitdiff/fb7890aedbd4d67bc1ddee65f9249f5b6ccc9d49

Modified Files
--------------
contrib/pg_upgrade/check.c |   92 --------------------------------------------
contrib/pg_upgrade/info.c  |    8 +++-
2 files changed, 7 insertions(+), 93 deletions(-)