pgsql: Set indcheckxmin true when REINDEX fixes an invalid or not-ready

Set indcheckxmin true when REINDEX fixes an invalid or not-ready index.

Per comment from Greg Stark, it's less clear that HOT chains don't conflict
with the index than it would be for a valid index. So, let's preserve the
former behavior that indcheckxmin does get set when there are
potentially-broken HOT chains in this case. This change does not cause any
pg_index update that wouldn't have happened anyway, so we're not
re-introducing the previous bug with pg_index updates, and surely the case
is not significant from a performance standpoint; so let's be as
conservative as possible.

Branch
------
master

Details
-------
http://git.postgresql.org/pg/commitdiff/9ad7e15507ffa14f51d80d6ae3ed942ea191826d

Modified Files
--------------
src/backend/catalog/index.c | 13 ++++++++++---
1 files changed, 10 insertions(+), 3 deletions(-)