wpdb: When flushing results on a mysqli connection, make sure that `wpdb::$dbh` is a valid mysqli connection handle.

Fixes a unit test failure introduced in [30297].

Fixes #28155.

Props soulseekah.


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git-svn-id: http://core.svn.wordpress.org/trunk@30298 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Improve localization for `WP_Date_Query` error strings.

* Don't create an extra variable for the string when it's only used once.
* Avoid using `<code>` HTML tags inside of translatable string.
* Improve data types and escaping on sprintfed values.

Props dd32.
Fixes #25834.
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git-svn-id: http://core.svn.wordpress.org/trunk@30299 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Correct grammar error in `WP_Date_Query` error message.

Props Offereins.
See #25834.
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git-svn-id: http://core.svn.wordpress.org/trunk@30300 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Twenty Fifteen: simpler CSS by using divs instead of spans for menu descriptions.

Props philiparthurmoore, fixes #30296


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Twenty Fifteen: create consistent spacing with embeds and images.

Props afercia, fixes #30286


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Twenty Fifteen: simplify the code used to generate screen reader text for the is_home title.

Props davidakennedy, fixes #30305


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Twenty Fifteen: Minor formatting and docs tweaks, clearer variable name.

Props celloexpressions, see #29988


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Customizer: When navigating around the site within the Customizer preview, update the document title.

props westonruter.
fixes #28542.
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Customizer: Use `jQuery.fn.toggle()` instead of `slideUp`/`slideDown` if panel/section/control is not inserted into DOM yet.

jQuery does nothing when calling `slideUp` on elements that are not inserted into the DOM yet, which can now be the case now when first loading the Customizer as the panels, sections and controls get dynamically inserted, see #28709.

props westonruter.
fixes #30251.
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Customizer: Trigger `widget-added` event when initializing.

Widget controls are now added to the pane dynamically via JavaScript, see #28709.
Remove the event trigger from `SidebarControl.addWidget()` as it's covered by `WidgetControl.ready()`.

props westonruter.
fixes #30236.
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git-svn-id: http://core.svn.wordpress.org/trunk@30307 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Customizer: Add support for the media library in Background Image controls.

`WP_Customize_Upload_Control` (PHP) and `api.UploadControl` (JS) can now open the media modal.

props celloexpressions, and ericlewis for docs.
see #21483.
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Always use a full filesystem path when including the FTP handler in PemFTP. This prevents other files in the includes directory being scanned/included accidentally.
See #29628

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PHP 5.2 compatibility for [30310], __DIR__ wasn't added until PHP 5.3. Props TobiasBg. Fixes #29628

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Twenty Fifteen: clean up sprintf from template tags and use the correct escaping for twentyfifteen template tags.

Props aprea, obenland, fixes #30319


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Use a brighter blue against dark backgrounds in the admin menu and toolbar.

Not only does this pass contrast guidelines, but it also visually appears closer to the original highlight blue used against light backgrounds.

props melchoyce. fixes #30323.

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git-svn-id: http://core.svn.wordpress.org/trunk@30312 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Twenty Fifteen: adding context to page links for screenreaders.

Props afercia, fixes #30174.


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Twenty Fifteen: since color schemes can be customized let's call them base color schemes instead of just color schemes.

Props celloexpressions, iandstewart, fixes #30316


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Twenty Fifteen: adding context to pagination links for screenreaders.

Props afercia, iamtakashi, fixes #30152


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Twenty Fifteen: improve appearance of page links when there are tons of pages to link to

Props iamtakashi, fixes #30301


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TinyMCE: enhance the inline toolbar for images:
- Add alignment (left, center, right, none) buttons.
- Position the menu above the image when possible, except on iOS.
- Fix selecting images on iOS.
First run, part props avryl. See #30147.
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