Limit metabox to specific page

gistfile1.aw

<?php
// Changes to metabox array, new field 'show_on'

	$meta_boxes[] = array(
    	'id' => 'blog-options',
	    'title' => 'Blog Options',
	    'pages' => array('page'), 
	    'show_on' => array( 'key' => 'id', 'value' => array( 12 ) ),
		'context' => 'normal',
		'priority' => 'low',
		'show_names' => true, 
		'fields' => array(
			array(
		        'name' => 'Query Arguments',
		        'desc' => '',
	    	    'id' => 'query_args',
	        	'type' => 'text'
			),
		),
	);


// Changes to init.php, new add() function
	function add() {
		$this->_meta_box['context'] = empty($this->_meta_box['context']) ? 'normal' : $this->_meta_box['context'];
		$this->_meta_box['priority'] = empty($this->_meta_box['priority']) ? 'high' : $this->_meta_box['priority'];
		foreach ( $this->_meta_box['pages'] as $page ) {
			if( !isset( $this->_meta_box['show_on'] ) ) {
				add_meta_box( $this->_meta_box['id'], $this->_meta_box['title'], array(&$this, 'show'), $page, $this->_meta_box['context'], $this->_meta_box['priority']) ;
			} else {
				if ( 'id' == $this->_meta_box['show_on']['key'] ) {
	
					// If we're showing it based on ID, get the current ID					
					if( isset( $_GET['post'] ) ) $post_id = $_GET['post'];
					elseif( isset( $_POST['post_ID'] ) ) $post_id = $_POST['post_ID'];

					// If current page id is in the included array, display the metabox
					if ( isset( $post_id) && in_array( $post_id, $this->_meta_box['show_on']['value'] ) )
						add_meta_box( $this->_meta_box['id'], $this->_meta_box['title'], array(&$this, 'show'), $page, $this->_meta_box['context'], $this->_meta_box['priority']) ;
				}
			}
		}
	}