PHP Notice in Contact Widget

With wp-config.php set as
define('WP_DEBUG', 1);
define('WP_DEBUG_LOG', 1);
define('WP_DEBUG_DISPLAY', 1);

The Contact Widget shows this PHP notice:
Notice: wp_enqueue_script was called incorrectly. Scripts and styles should not be registered or enqueued until the wp_enqueue_scripts, admin_enqueue_scripts, or init hooks. Please see Debugging in WordPress for more information.

A quick backtrace shows:
Array
(
[0] => Array
(
[file] => wp-includes/functions.wp-scripts.php
[line] => 130
[function] => _doing_it_wrong
[args] => Array
(
[0] => wp_enqueue_script
[1] => Scripts and styles should not be registered or enqueued until the wp_enqueue_scripts, admin_enqueue_scripts, or init hooks.
[2] => 3.3
)

)

[1] => Array
(
[file] => wp-content/plugins/contact-form/contact-form.php
[line] => 30
[ in wp-includes/functions.php on line 2960

The problem is in
wp-content/plugins/contact-form/contact-form.php line 30:
wp_enqueue_script("jquery");

It should be called from within other wp_* calls, not directly. See http://plugins.trac.wordpress.org/changeset/655287 for an example, and also http://stackoverflow.com/questions/11336578/wp-debug-errors-with-wp-enqueue