Introduce `get_previous_post_link()`, `get_next_post_link()`, and `get_adjacent_post_link()`. Allows developers to retrieve the value without `echo`ing.

Props yoavf, markjaquith, SergeyBiryukov.
Fixes #17302.


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git-svn-id: http://core.svn.wordpress.org/trunk@25289 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Add filter `flush_rewrite_rules_hard` to give devs chance to prevent writing to file when hard-flushing rewrite rules.

Props jeremyfelt, nacin.
Fixes #23491.


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git-svn-id: http://core.svn.wordpress.org/trunk@25290 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Add an additional available param (the `WP_User` instance) to the `user_has_cap` filter.

Props Viper007Bond.
Fixes #24490.


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git-svn-id: http://core.svn.wordpress.org/trunk@25291 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Check `$profileuser->rich_editing` for empty before using it in Edit User admin code.

Props sorich87, c3mdigital.
Fixes #17328.


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git-svn-id: http://core.svn.wordpress.org/trunk@25292 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Support `orderby => meta_value` in `WP_User_Query`. Adds unit test.

Props wpsmith.
Fixes #21581.


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git-svn-id: http://core.svn.wordpress.org/trunk@25293 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Use `wp_get_nav_menus()` instead of `get_terms('nav_menu')` in `WP_Nav_Menu_Widget` to preserve use of `wp_get_nav_menus' filter.

Props Frank Klein.
Fixes #25263.


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git-svn-id: http://core.svn.wordpress.org/trunk@25294 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Remove dead code in `add_query_arg()`.

Props hakre, c3mdigital.
Fixes #16942.


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git-svn-id: http://core.svn.wordpress.org/trunk@25295 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Add `term_taxonomy_id` to available fields in `get_term_by()`. Adds unit test.

Props jchristopher.
Fixes #21651.


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git-svn-id: http://core.svn.wordpress.org/trunk@25296 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Don't call `sanitize_title_with_dashes( $taxonomy )` in `register_taxonomy()` unless `$args['rewrite']['slug']` is empty.

Props SergeyBiryukov.
Fixes #23668.


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git-svn-id: http://core.svn.wordpress.org/trunk@25297 1a063a9b-81f0-0310-95a4-ce76da25c4cd