Introduce initial_db_version and leverage it so that pointers only get shown...

Introduce initial_db_version and leverage it so that pointers only get shown to updated installs, not new 3.3 installs. props nacin. see #18693

git-svn-id: https://core.svn.wordpress.org/trunk@19410 1a063a9b-81f0-0310-95a4-ce76da25c4cd