Remove redundant assignment. see [28379], [28534].

see #22400.
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git-svn-id: http://core.svn.wordpress.org/trunk@28364 1a063a9b-81f0-0310-95a4-ce76da25c4cd
These functions import `$wpdb` but do not use it.

See #27882.

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git-svn-id: http://core.svn.wordpress.org/trunk@28365 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Use correct variable. see [28534], [28538].

see #22400.
Built from https://develop.svn.wordpress.org/trunk@28540


git-svn-id: http://core.svn.wordpress.org/trunk@28366 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Apply `order` to each passed value for `orderby` in `WP_Query`:

* Since `orderby` in `WP_Query` can accept space-delimited sets, yet only one `order` value: when multiple values are passed (and `DESC` is the order), the default sort order `ASC` is being applied to all values before the last in the set.
* There is a unit test that sporadically fails since 3.6 in `tests/post/revision` due to multiple posts having the same `post_date` from being added so rapidly
* When ordering revisions in `wp_get_post_revisions()`, order by `post_date ID`
* Change the `order` value in `wp_get_post_revisions()` to `ASC`. This will produce SQL like: `ORDER BY $wpdb->posts.post_date ASC, $wpdb->posts.ID ASC`. Previously, this would have produced SQL like: `ORDER BY $wpdb->posts.post_date DESC`, and with the addition of ` ID`: `ORDER BY $wpdb->posts.post_date ASC, $wpdb->posts.ID DESC`. Clearly, wrong. The original SQL produced: `ORDER BY $wpdb->posts.post_date DESC`. As such, return the reversions in reverse order using `array_reverse()`. Not doing so would break "Preview Changes."
* Add unit tests to assert that all of this works.
* All existing unit tests pass with the change to ordering multiple `orderby`s in `WP_Query`.
* In the future, we should support independent `order` for each `orderby`, see #17065.

Props SergeyBiryukov, wonderboymusic.
Fixes #26042.

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git-svn-id: http://core.svn.wordpress.org/trunk@28367 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Because PHP can be configured without `--filter`, it is not 100% safe to use `filter_var()`. This is problematic for casting `"false"` to `false`, as PHP always casts it to `true`. `FILTER_VALIDATE_BOOLEAN` fixes this, but it may not be available.

Add a new function, `wp_validate_boolean()`, to replace `filter_var( $var, FILTER_VALIDATE_BOOLEAN )`.

Fixes #28170.


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git-svn-id: http://core.svn.wordpress.org/trunk@28368 1a063a9b-81f0-0310-95a4-ce76da25c4cd