Add #actions container to submit buttons

Problem/Motivation

I've experienced minor problem when styling Execute PHP admin form because it doesn't have #actions container, which is common practice in all admin forms.

Proposed resolution

Add 'actions' parent level to 'Execute' button. Change:

$form['execute']['op'] = array('#type' => 'submit', '#value' => t('Execute'));

to:

$form['execute']['actions'] = array('#type' => 'actions');
$form['execute']['actions']['op'] = array('#type' => 'submit', '#value' => t('Execute'));

Remaining tasks

n/a

User interface changes

Button will follow admin theme standards, ex. in 'Seven' will be aligned to the right.

API changes

n/a