pgsql: Update documentation to mention that autovacuum also does analyze

Log Message:
-----------
Update documentation to mention that autovacuum also does analyze so we
don't need to recommend nightly analyzes anymore unless autovacuum is off.

Modified Files:
--------------
pgsql/doc/src/sgml:
maintenance.sgml (r1.80 -> r1.81)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/maintenance.sgml?r1=1.80&r2=1.81)