This will do it:
function edit_screen_title() {
global $post, $title, $action, $current_screen;
if( isset( $current_screen->post_type ) && $current_screen->post_type == 'post' && $action == 'edit' )
$title="Edit " . $post->post_title;
}
add_action( 'admin_head', 'edit_screen_title' );