Multisite load: Cache the main site lookup query.

props jeremyfelt.
see #27003.

Built from https://develop.svn.wordpress.org/trunk@27664


git-svn-id: http://core.svn.wordpress.org/trunk@27507 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Use wp_cache_add() instead of wp_cache_set() when we don't want an unconditional set.

props jeremyfelt.
see #27003.

Built from https://develop.svn.wordpress.org/trunk@27665


git-svn-id: http://core.svn.wordpress.org/trunk@27508 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Inline documentation for hooks in wp-includes/category-template.php.

Props kpdesign for the cleanup.
Fixes #27432.

Built from https://develop.svn.wordpress.org/trunk@27666


git-svn-id: http://core.svn.wordpress.org/trunk@27509 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Inline documentation for hooks in wp-admin/includes/post.php.

Also moves the primary PHPDoc for the `edit_posts_per_page` hook to wp-admin/includes/post.php.

Props kpdesign for some cleanup.
Fixes #27431.

Built from https://develop.svn.wordpress.org/trunk@27667


git-svn-id: http://core.svn.wordpress.org/trunk@27510 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Introduce HTML5 caption support.

When a theme supports HTML5 captions via add_theme_support( 'html5', 'caption' ), figure and figcaption will be used instead of div and p.

There's a bonus. But first, some history: Captions were introduced with an inline style set for the container. This remains, as it is there to force captions to wrap. But this inline style included an extra 10 pixels, which have vexxed theme developers for years. While these pixels were designed to ensure padding around floated images, modern themes handle this with grace. The additional pixels thus feel encumbering.

As the new HTML5 gallery support avoids outputting default gallery styles (again, irking theme developers for years; see #26697), the new HTML5 caption support will also ditch these 10 pixels of unwanted hand-holding. 

The 10 pixels are also removed entirely in the visual editor (and more styles may also disappear here; see #26642), giving themes the power necessary to match the frontend styles.

The filter img_caption_shortcode_width added in 3.7 to work around this madness (see #14380) is skipped entirely when the theme supports HTML5 captions.

props obenland, azaozz.
see #26642. also fixes #9066.

Built from https://develop.svn.wordpress.org/trunk@27668


git-svn-id: http://core.svn.wordpress.org/trunk@27511 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Inline documentation for hooks in wp-admin/includes/dashboard.php.

Props mauryaratan. Props kpdesign for some minor cleanup.
Fixes #25752.

Built from https://develop.svn.wordpress.org/trunk@27669


git-svn-id: http://core.svn.wordpress.org/trunk@27512 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Inline documentation for hooks in wp-admin/includes/menu.php.

Also fixes syntax for a few unrelated multi-line comments in the file.

Props kpdesign for some minor cleanup.
Fixes #27430.

Built from https://develop.svn.wordpress.org/trunk@27670


git-svn-id: http://core.svn.wordpress.org/trunk@27513 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Remove some debug cruft accidentally committed in [27670].

See #27430.

Built from https://develop.svn.wordpress.org/trunk@27671


git-svn-id: http://core.svn.wordpress.org/trunk@27514 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Inline documentation for hooks in wp-admin/includes/file.php.

Fixes #27429.

Built from https://develop.svn.wordpress.org/trunk@27672


git-svn-id: http://core.svn.wordpress.org/trunk@27515 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Inline documentation for wp-admin/includes/class-wp-upgrader.php.

Props kpdesign for some minor cleanup.
Fixes #27436.

Built from https://develop.svn.wordpress.org/trunk@27673


git-svn-id: http://core.svn.wordpress.org/trunk@27516 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Inline documentation for hooks in wp-admin/includes/taxonomy.php.

Props kpdesign for the initial patch.
Fixes #27433.

Built from https://develop.svn.wordpress.org/trunk@27674


git-svn-id: http://core.svn.wordpress.org/trunk@27517 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Use correct variable. see [27373].

props TobiasBg.
fixes #14424.

Built from https://develop.svn.wordpress.org/trunk@27675


git-svn-id: http://core.svn.wordpress.org/trunk@27518 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Inline documentation for hooks in wp-includes/post-template.php.

Props Toru and kpdesign.
Fixes #25621.

Built from https://develop.svn.wordpress.org/trunk@27676


git-svn-id: http://core.svn.wordpress.org/trunk@27519 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Plugin Installer: Disable 'Latest Version Installed' buttons.

props paulwilde.
see #26952.

Built from https://develop.svn.wordpress.org/trunk@27677


git-svn-id: http://core.svn.wordpress.org/trunk@27520 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Ensure Thickbox loading spinner is properly sized for HiDPI displays.

props paulwilde.
see #26952.

Built from https://develop.svn.wordpress.org/trunk@27678


git-svn-id: http://core.svn.wordpress.org/trunk@27521 1a063a9b-81f0-0310-95a4-ce76da25c4cd