Use theme_image() for site logo

Currently, the Site Logo content type creates the <img> tag HTML, rather than using theme('image'). The latter allows themes to alter the image with hook_preprocess_image().

This is a simple change from:

$image = '<img src="' . $logo . '" alt="' . t('Home') . '" />';

to:

$image = theme('image', array('path' => $logo, 'alt' => t('Home')));