Don't use variable variables in `plugins_url()`.

See #27881.

Built from https://develop.svn.wordpress.org/trunk@28739


git-svn-id: http://core.svn.wordpress.org/trunk@28553 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Don't use variable variables in `wp_insert_user()`. 
Add a local array, `$meta`, to provide substantial disambiguation among variables. 

See #27881.

Built from https://develop.svn.wordpress.org/trunk@28740


git-svn-id: http://core.svn.wordpress.org/trunk@28554 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Don't use variable variables in `wp_salt()`.

See #27881.

Built from https://develop.svn.wordpress.org/trunk@28741


git-svn-id: http://core.svn.wordpress.org/trunk@28555 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Don't use variable variables in `wp_dashboard_plugins_output()`. Variable variables aren't the worst thing about this function.

See #27881.

Built from https://develop.svn.wordpress.org/trunk@28742


git-svn-id: http://core.svn.wordpress.org/trunk@28556 1a063a9b-81f0-0310-95a4-ce76da25c4cd