Change ANALYZE to take ShareUpdateExclusiveLock not AccessShareLock on

Change ANALYZE to take ShareUpdateExclusiveLock not AccessShareLock on
the table being analyzed.  This prevents two ANALYZEs from running
concurrently on the same table and possibly suffering concurrent-update
failures while trying to store their results into pg_statistic.  The
downside is that a database-wide ANALYZE executed within a transaction
block will hold ShareUpdateExclusiveLock on many tables simultaneously,
which could lead to concurrency issues or even deadlock against another
such ANALYZE.  However, this seems a corner case of less importance
than getting unexpected errors from a foreground ANALYZE when autovacuum
elects to analyze the same table concurrently.  Per discussion.