Post thumbnails should not be affected by $content_width

[Viper007Bond]

set_post_thumbnail_size( 940, 198, true );
$content_width = 640;
the_post_thumbnail();

Outputs something like this:

<img width="640" height="134" src=".../filename-940x198.png" class="attachment-post-thumbnail wp-post-image" alt="" title="title" />

Note that the thumbnail is being generated correctly, but the HTML width/height is being affected by $content_width. This should not happen. If a theme author wants it to not be wider than the theme width, then they wouldn't have set the width to be wider. Post thumbnails can be used outside of the content area.

A good example of this is the 2010 theme which uses a post's thumbnail as the header image in single post view.

Do only post thumbnails use $_wp_additional_image_sizes ?

(In [13103]) Do not limit thumbnails by the content_width. props Viper007Bond. fixes #12146

Unintended side-effect: post thumbnail preview on write screen is not downsized to fit. The meta box is was setting $content_width before to make it fit.

Rather than adding some other variable/global to replicate the old method, I think it'd just be easier to regex the HTML and modify the width/height.

Use a bit of a hack to make the thumbnail fit in the meta box

(In [13140]) Revert r13103 and merely restrict \$content_width obeying to is_admin(). fixes #12146