Add last-vacuum/analyze-time columns to the stats collector, both manual and

Add last-vacuum/analyze-time columns to the stats collector, both manual and
issued by autovacuum.  Add accessor functions to them, and use those in the
pg_stat_*_tables system views.

Catalog version bumped due to changes in the pgstat views and the pgstat file.

Patch from Larry Rosenman, minor improvements by me.