Customizer: Ensure we have a string that's JSON parseable.

props mattwiebe.
fixes #postmessage-check.diff.

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Return false from wp_delete_post() and wp_delete_attachment() if the DELETE is unsuccessful.

This prevents attachments from being deleted off disk when a DB is locked and the delete is otherwise unsuccessful.

fixes #25107.

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Be specific in term_exists error messages in wp_insert_term() as to what already exists (name, or name and slug).

props ericmann, SergeyBiryukov.
fixes #15741.

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Twenty Fourteen: use a more specific selector for tag links.

props iamtakashi.
fixes #26358.
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Add dashicons CSS classes for easy access by plugins and themes.

props dd32.
fixes #26227.

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Customizer: Don't trigger a change event if two unchanged object values are equal.

In JavaScript: `{"title":"Foo"} !== {"title":"Foo"}`
Underscore.js provides an isEqual function to compare two values to see if they have the same contents, which can be use instead.
Because only one function of Underscore.js is needed we just add a copy of `_.isEqual` to customize-base.js.

props westonruter.
fixes #26061.
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Heartbeat:
- Bring back heartbeat.interval().
- Rename wp_disable_heartbeat_suspend() to wp_heartbeat_set_suspension().
- Rename the option for disabling suspension from options.suspend to options.suspension.
Fixes #25073.
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Comments moderation screen:
- Don't resize the textarea when replying to long comments.
- Limit the resizing of the textarea when quick-editing long comments to 500px.
Props SergeyBiryukov, fixes #25746.
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Themes: Update the CSS definitions in the SCSS files to be as specific as the base CSS rules. See #25948, #25966

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Quicktags: fix int/string strict comparison, see #26046.
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Remove unnecessary padding on welcome panel icons at responsive sizes. Fixes #26374, props mattheu.
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Twenty Fourteen: limit Help tab text to only "post" post type edit screen. Props obenland, see #25837.
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Twenty Fourteen: update comment blocks to match inline docs standards. Props DrewAPicture, see #25837.
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Revert [26050], stop trying to balance open HTML tags across nextpage and more tags for now.

see #6297.

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Twenty Fourteen: make sure non-breaking title in `.nav-links` doesn't overflow, and make sure the menu toggle text is hidden. Props iamtakashi, closes #26189.
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Give the adminbar Edit Post link an icon, and make it visible on small screen responsive states. See #26071.


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Twenty Fourteen: code cleanup, props kovshenin. See #25946.

 * Filtering `twentyfourteen_has_featured_posts()` false suggests the filter expects a boolean value, but we expect an array. Use an existing function instead.
 * In both style.css and ie.css use Genericons, so let's not forget to declare the dependancy.
 * Make sure Lato font is enqueued in `admin_print_scripts`.
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Twenty Fourteen: update editor stylesheet to reflect recent changes made in the main stylesheet. Props iamtakashi, see #25946.
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Twenty Fourteen: tweak the vertical space for list items in the primary and footer widgets. Props iamtakashi, see #25946.
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Better Dashboard treatment when in no-JS, especially Quick Draft. props georgestephanis, helen. fixes #26376.

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