pgsql: In the new dispensation where REINDEX doesn't take exclusive lock

Log Message:
-----------
In the new dispensation where REINDEX doesn't take exclusive lock on
the parent table, it's essential that all index accesses take some kind
of lock on the index.  I had missed vacuumlazy.c :-( ...

Modified Files:
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    pgsql/src/backend/commands:
        vacuumlazy.c (r1.47 -> r1.48)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/commands/vacuumlazy.c.diff?r1=1.47&r2=1.48)