Controls need public $type property

[michaeldcain]

Per Otto's explanation, each custom control should probably declare a unique public $type property.

Example:

if ( ! class_exists( 'WP_Customize_Control' ) )
    return NULL;

class Textarea_Custom_Control extends WP_Customize_Control
{
    public $type = 'textarea';

    /**
     * Render the control's content.
     *
     * Allows the content to be overriden without having to rewrite the wrapper.
     *
     * @since   10/16/2012
     * @return  void
     */
    public function render_content() {