Default image alignment setting doesn't select a default radio button

[MtDewVirus]

Default image alignment from Settings->Miscellaneous doesn't select a default radio button. Use 'None' as the default.

[ryan]

(In [8713]) Default image alignment setting doesn't select a default radio button. Props MtDewVirus. fixes #7574

[AaronCampbell]

Shouldn't we be using the checked function here? (from wp-admin/includes/template.php)