Core Updates: Fix a case where options (db_version specifically) can end up with stale values in the cache after a update is performed.

Merges [26448] and [26734] from 3.8 to the 3.7 branch.

props dd32.
fixes #26173.

Built from https://develop.svn.wordpress.org/branches/3.7@27885


git-svn-id: http://core.svn.wordpress.org/branches/3.7@27716 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-admin/includes/update-core.php

@@ -886,6 +886,11 @@ function update_core($from, $to) {
 	$db_upgrade_url = admin_url('upgrade.php?step=upgrade_db');
 	wp_remote_post($db_upgrade_url, array('timeout' => 60));
 
+	// Clear the cache to prevent an update_option() from saving a stale db_version to the cache
+	wp_cache_flush();
+	// (Not all cache backends listen to 'flush')
+	wp_cache_delete( 'alloptions', 'options' );
+
 	// Remove working directory
 	$wp_filesystem->delete($from, true);