One thing fairly common to the cache groups is a block of code to look to see when the cache was last changed, and if there isn't one, to set it for the current microtime(). It appears in 8 different places in core. This adds a new helper `wp_cache_get_last_changed` to DRY things up a bit.
Since `wp-includes/cache.php` isn't guaranteed to be loaded, this new function is in `wp-includes/functions.php`
Props spacedmonkey, desrosj.
Fixes#37464.
git-svn-id: https://develop.svn.wordpress.org/trunk@38849 602fd350-edb4-49c9-b593-d223f7449a82
Hiding the `$wpdb` global behind a property decreases the readability of the code, as well as causing irrelevant output when dumping an object.
Reverts [38275], [38278], [38279], [38280], [38387].
See #37699.
git-svn-id: https://develop.svn.wordpress.org/trunk@38768 602fd350-edb4-49c9-b593-d223f7449a82
Provides a consistent way to query `$wpdb->site` for `WP_Network` objects based on domain, path, network ID, and (main) site ID.
Introduces and uses update_network_cache() and _prime_network_caches() to maintain a cached list of WP_Network objects for use in multiple queries.
Props flixos90.
See #32504.
git-svn-id: https://develop.svn.wordpress.org/trunk@37894 602fd350-edb4-49c9-b593-d223f7449a82
