pgsql: Fix table lock levels for REINDEX INDEX CONCURRENTLY

Fix table lock levels for REINDEX INDEX CONCURRENTLY

REINDEX CONCURRENTLY locks tables with ShareUpdateExclusiveLock rather
than the ShareLock used by a plain REINDEX.  However,
RangeVarCallbackForReindexIndex() was not updated for that and still
used the ShareLock only.  This would lead to lock upgrades later,
leading to possible deadlocks.

Reported-by: Andres Freund <andres@anarazel.de>
Reviewed-by: Andres Freund <andres@anarazel.de>
Reviewed-by: Michael Paquier <michael@paquier.xyz>
Discussion: https://www.postgresql.org/message-id/flat/20190430151735.wi52sxjvxsjvaxxt%40alap3.anarazel.de

Branch
------
master

Details
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https://git.postgresql.org/pg/commitdiff/add85ead4ab969c1e31d64f4476c2335856f4aa9

Modified Files
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src/backend/commands/indexcmds.c | 45 +++++++++++++++++++++++++++++-----------
1 file changed, 33 insertions(+), 12 deletions(-)