Don't include the default columns="3" in a gallery shortcode.

Shortcode attributes are strings; fix a variable type error in wp.media.gallery defaults.
props adamsilverstein.

see #22919.
Ensure that get_archive_template() only loads a post type archive (archive-$post_type.php file) if there is exactly one post type in the query.

props scribu.
see #22956.
for trunk.
Upgrade: When upgrading from WordPress 3.5, if an empty twentytwelve theme directory exists, remove it to allow the installation of Twenty Twelve. See #22856. For trunk
Clarify the Documentation in win_is_writable() and move an inline comment to the Docblock, reduces confusion about what the function actually does. See #22900