REST API

Add a caveat if we get back a WP_Error.

Props @justinshreve

ref 92567
REST API: add xmlrpc to a site's meta.links

We need a reference to a site's XML-RPC URL for the mobile apps until
we move to using only REST.
The XML-RPC endpoint can't be inferred from URL because of mapped
domains.

Props @koke
REST API: Track API errors that we return.

Props @justinshreve
Publicize Media Summary --

Add an extra if check to catch galleries.

Props @justinshreve, ref 91750
Twitter Cards: Add in twitter:site

Allow customization of the `twitter:site` setting via the twitter via
setting.

Thanks to @mjangda for the suggestion.

Props @justinshreve, ref 92129
locales.php - Add Irish!

Add the wp_locale for irish.

Props @westi, @nacin

See: https://glotpress.trac.wordpress.org/changeset/831
locales: Merge r823-glotpress

Add support for Fulah

See: https://glotpress.trac.wordpress.org/changeset/823

Props @zedejose
locales: merge r830-glotpress

Add support for Tigrinya, per
http://en.forums.wordpress.com/topic/language-list

See: https://glotpress.trac.wordpress.org/changeset/830

Props @zedejose
Swapping to the wpcom minified versions of the images.
Bump Carousel RTL stylesheet!
Media Extractor: separate code for image extraction

Separate code for image extraction into a separate call so we can
extract images from comments.

Props @gibrown, ref 90980
Social Links: Remove links to disconnected services

Props @obenland, ref 90419
Featured Content: Hide term based on term name rather than term id.

Since only the term name gets updated by the Customizer, the term_id
will not always be correct during preview. This might lead to confusion
when the previewed term is still visible, even though it is supposed to
be hidden.

Props @obenland, ref 90228
Correct CSS property.
Infinite Scroll: GET -> POST

Switch from GET to POST in the JS, and in the PHP use $_REQUEST to
handle either.  URL request strings were (in rare circumstances)
getting too long and running out of room.  POST will never face that
difficulty.
Publicize: Add font-size CSS.

Also, bump the RTL stylesheet.
Merge pull request #273 from Automattic/wpcom-merge

Merge changes in from WordPress.com [upstream]