function dr_email_login_authenticate( $user, $username, $password ) {
    if ( is_a( $user, 'WP_User' ) )
        return $user;

    if ( !empty( $username ) ) {
        $username = str_replace( '&', '&', stripslashes( $username ) );
        $user = get_user_by( 'email', $username );
        if ( isset( $user, $user->user_login, $user->user_status ) && 0 == (int) $user->user_status )
            $username = $user->user_login;
    }

    return wp_authenticate_username_password( null, $username, $password );
}
remove_filter( 'authenticate', 'wp_authenticate_username_password', 20, 3 );
add_filter( 'authenticate', 'dr_email_login_authenticate', 20, 3 );