Fix some `hackificator` odds and ends in `wp-admin`:

* `wp-activate.php` and `wp-admin/themes.php` don't need the closing PHP tag
* Switch single quotes for HTML attribute values to double in a few places
* Convert `include_once file.php` syntax to `include_once( 'file.php' )`
* Add access modifiers to methods/members in: `_WP_List_Table_Compat`, `Walker_Nav_Menu_Edit`, `Walker_Nav_Menu_Checklist`, `WP_Screen`, `Walker_Category_Checklist`
* `edit_user()` doesn't need to import the `$wpdb` global
* `wp_list_widgets()` doesn't need to import the `$sidebars_widgets` global
* switch/endswitch syntax is not supported in Hack
* A `<ul>` in `wp-admin/users.php` is unclosed

See #27881.

Built from https://develop.svn.wordpress.org/trunk@28500


git-svn-id: http://core.svn.wordpress.org/trunk@28326 1a063a9b-81f0-0310-95a4-ce76da25c4cd
In `wp_list_bookmarks()`, `$categorize` should now be `$r['categorize]`.

See #22400.

Built from https://develop.svn.wordpress.org/trunk@28501


git-svn-id: http://core.svn.wordpress.org/trunk@28327 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Add access modifiers to methods/members in `WP_Object_Cache`. Add a magic `__get()` method for BC.

See #27881.

Built from https://develop.svn.wordpress.org/trunk@28502


git-svn-id: http://core.svn.wordpress.org/trunk@28328 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Add access modifiers to methods/members in `WP_Roles`. Add a magic `__call()` method for BC.

See #27881, #22234.

Built from https://develop.svn.wordpress.org/trunk@28503


git-svn-id: http://core.svn.wordpress.org/trunk@28329 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Add access modifiers to methods/members in `Walker_Category` and `Walker_CategoryDropdown`.

See #27881, #22234.

Built from https://develop.svn.wordpress.org/trunk@28504


git-svn-id: http://core.svn.wordpress.org/trunk@28330 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Add access modifiers to methods/members in `WP_Feed_Cache`, `WP_SimplePie_File`, and `WP_Feed_Cache_Transient`.

See #27881, #22234.

Built from https://develop.svn.wordpress.org/trunk@28505


git-svn-id: http://core.svn.wordpress.org/trunk@28331 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Add access modifier to methods of HTTP classes. There are no new private or protected methods, so no need for `__call()`.

 See #27881, #22234.

Built from https://develop.svn.wordpress.org/trunk@28506


git-svn-id: http://core.svn.wordpress.org/trunk@28332 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Add access modifier to methods/members in `WP_oEmbed`. Adds a magic `__call()` method for BC.

See #27881, #22234.

Built from https://develop.svn.wordpress.org/trunk@28507


git-svn-id: http://core.svn.wordpress.org/trunk@28333 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Add access modifier to methods/members in `WP_Ajax_Response`. Adds a magic `__get()` method for BC.

See #27881, #22234.

Built from https://develop.svn.wordpress.org/trunk@28508


git-svn-id: http://core.svn.wordpress.org/trunk@28334 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Add missing access modifiers to methods/members in `WP_Customize_*`.

See #27881, #22234.

Built from https://develop.svn.wordpress.org/trunk@28509


git-svn-id: http://core.svn.wordpress.org/trunk@28335 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Add access modifiers to methods/members in `WP_Embed`.

See #27881, #22234.

Built from https://develop.svn.wordpress.org/trunk@28510


git-svn-id: http://core.svn.wordpress.org/trunk@28336 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Add access modifiers to methods/members in `WP_Error`. Add a magic `__get()` method for BC.

See #27881, #22234.

Built from https://develop.svn.wordpress.org/trunk@28511


git-svn-id: http://core.svn.wordpress.org/trunk@28337 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Add access modifiers to methods/members in `WP_HTTP_IXR_Client`.

See #27881, #22234.

Built from https://develop.svn.wordpress.org/trunk@28512


git-svn-id: http://core.svn.wordpress.org/trunk@28338 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Add missing access modifiers to methods/members in `WP_Image_Editor_*` classes.

See #27881, #22234.

Built from https://develop.svn.wordpress.org/trunk@28513


git-svn-id: http://core.svn.wordpress.org/trunk@28339 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Add missing access modifiers to methods/members in `Walker` and subclasses. Add a magic `__get()` method.

See #27881, #22234.

Built from https://develop.svn.wordpress.org/trunk@28514


git-svn-id: http://core.svn.wordpress.org/trunk@28340 1a063a9b-81f0-0310-95a4-ce76da25c4cd