Use ImageOptim to losslessly smush our images. About half a MB in savings! fixes #22381. props waldojaquith
Display links if no link categories exist. props MikeHansenMe. fixes #22216.
Extend Press This by a few pixels to allow longer strings. props SergeyBiryukov. fixes #20975.
Remove single-argument calls to wpdb:prepare(), which are invalid as nothing is being prepared. see #22262.
Enforce a minimum of two arguments for wpdb::prepare(). The first argument is the query (or fragment thereof), which is required. Additional arguments are values to substitute into placeholders.

This will generate E_WARNINGs for insufficient arguments when prepare() is called with no additional arguments. This should discourage improper uses of prepare() under the guise of safely running a query.

props xknown. fixes #22262.
Merge some strings. props pavelevap. fixes #22306.
Don't return encoded ampersands from get_post_comments_feed_link() to avoid canonical redirect issues. Apply esc_url() when appropriate.

props markjaquith, SergeyBiryukov. fixes #21841.
Align the check column on the Updates screen. props ocean90. fixes #22339.
Only call wp_get_object_terms() if get_object_term_cache() says there is no cache (false), which is different than no terms. props wonderboymusic, fixes #16505.
Don't assign wp_the_query to wp_query by reference. Removing the ref avoids accidentally stomping wp_the_query.

Props scribu, wpmuguru
fixes #22125
Avoid an uncaught exception in get_gmt_from_date(). The return value is imperfect - date( $format, 0 ) - but better than a fatal error. props wonderboymusic. fixes #20942.
Allow get_custom_header() to handle a default registered header that has yet to be saved to the database. fixes #22221.
Media: Integrate the gallery workflow with the media menu.

`wp.media.model.Query.more()`
* If a request has already been sent out for more attachments, return that request object instead of creating another.

`wp.media.controller.Region`
* A region allows views to be swapped in and out of a section of the page without either view having to know about the other.
* Application components can use the same callbacks and resources by leveraging `Region.mode()`, which triggers a set of callbacks to create or transform the current view, but only if necessary.

`wp.media.view.Frame`
* Leverage `Region` controllers instead of forcing states to swap view objects, which causes states to fit more comfortably in the controller-camp.
* Add `previous()`, a method to fetch the previous state `id`.
* Separate out the default settings over several objects (so blank frames can be instantiated).

`wp.media.view.MediaFrame`
* The base `Frame` used for media management: handles integration with the `Modal` and `UploaderWindow` views.

`wp.media.view.MediaFrame.Post`
* Includes all default media states and callbacks necessary for inserting media into a post.

see #21390.
Compress scripts/styles: 3.5-beta2-22438. TinyMCE updated.
More retina backgrounds and bits, props saracannon, empireoflight and lessbloat, see #21019
Allow the .hidden class to hide a button. props helenyhou. fixes #22018.
Update the old wp-app.php rule to allow for a trailing slash followed by endpoint data. props wonderboymusic. fixes #22035.
Post UI: Provide visual feedback to the user if they try to set an invalid date for a post. Fixes #17180 props jkudish.
Try to avoid overflow of the page template dropdown with long template names. props SergeyBiryukov, ocean90. fixes #21956.
Put the label outside the span to ensure margins when the text wraps. props waclawjacek. fixes #19254.