Split shared taxonomy terms during term update.

When updating an existing taxonomy term that shares its `term_id` with
another term, we generate a new row in `wp_terms` and associate the updated
term_taxonomy_id with the new term. This separates the terms, such that
updating the name of one term does not change the name of any others.

Note that this term splitting only occurs on installations whose database
schemas have been upgraded to version 30133 or higher. Note also that shared
terms are only split when run through `wp_update_term()`, as on edit-tags.php;
we will wait until a future release of WordPress to force the splitting of all
shared taxonomy terms.

Props boonebgorges, rmccue, greuben, garyc40, wonderboymusic, imath, jesin.
Fixes #5809.
Built from https://develop.svn.wordpress.org/trunk@30241


git-svn-id: http://core.svn.wordpress.org/trunk@30241 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Create new $wp_roles object in install_blog() to avoid protected _init() call

Our call to `$wp_roles->_init()` relied on the `__call()` method in `WP_Roles` to handle the link to the protected method. This works back to PHP 5.2.9, when a bug was fixed allowing access to protected methods through this exact approach.

`install_blog()` needs a fresh `$wp_roles` object after `populate_roles()` resets everything in its path. We can create this new object from scratch, effectively doing the same thing with the call to `_init()` via the constructor.

Fixes #29692 for trunk.

Built from https://develop.svn.wordpress.org/trunk@30242


git-svn-id: http://core.svn.wordpress.org/trunk@30242 1a063a9b-81f0-0310-95a4-ce76da25c4cd