Make use of the recursive option in mkdir() in wp_mkdir_p(). Avoids a bunch of silenced PHP Notices being logged. Fixes #23196

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WP_Upgrader: Don't activate maintenance mode in bulk_upgrade() when no Themes or Plugins are specified. This doesn't affect Core, but rather, plugins who use the upgrade routines and do not do precautionary tests. Props jamescollins. Fixes #24496

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Flush the cache in Recent Comments widget on edit_comment. props pento, fixes #24779.
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Introduce save_post_{$post_type} hook.

The hook is fired before the general save_post hook and has the same args as save_post.

props bmb, SergeyBiryukov, ocean90, fixes #16176.
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WP_HTTP: Curl: When using Stream-to-file on servers using mbstring.func_overload ensure that the file is written out correctly. Props DrProtocols. See #25061 for trunk

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