Automatic Updates: Skip doing the sanity checking MD5 before deciding if we should use a partial build or not, This change means we always use a partial build for automatic updates. See #22704

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MD5 file verification: Prevent md5_file() warnings when files don't exist, additionally, don't verify wp-content files as they can be updated separately, as well as WP_CONTENT_DIR being set elsewhere. See #22704 See #18201

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Automatic Updates: Add a rollback functionality upon installation failure, the rollback package will be available for partial-updates for automatic updates and be similar to our existing partial builds (but in reverse).
A further iteration of this is to also detect whitescreens (fatals) after a auto update, and trigger the rollback for that too.
See #22704

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Automatic Updates: Disable Automatic updates for Mercurial(HG) and Bazaar(bzr) version control systems in addition to Git and SVN. Props jamescollins. See #22704

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Automatic Updates: Remove some debug from [25649] See #22704

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