Make `has_shortcode()` recursive/work for nested shortcodes.

Adds unit test.

Props katzwebdesign.
Fixes #26343.

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Make sure that the `ready` event only fires once for relevant MCE views that are sandbox'd in iframes. Move some editor callbacks to `initialize`.

Props avryl.
See #28905.

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git-svn-id: http://core.svn.wordpress.org/trunk@28982 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Fix a typo in the `@access` tag for `WP_List_Table::__get()`.

Props joehoyle.
Fixes #28925. See #28885.

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git-svn-id: http://core.svn.wordpress.org/trunk@28983 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Properly set `$subdomain_error` to `false` when applicable in `ms_subdomain_constants()`. This was previously untestable because it used static vars: use globals instead.

Adds unit test.
Fixes #28697.

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git-svn-id: http://core.svn.wordpress.org/trunk@28984 1a063a9b-81f0-0310-95a4-ce76da25c4cd
In Plugin Install List Table, remove title attribute for plugin action links; add screen-reader-text.

Props joedolson.
Fixes #28853.

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