Automatically resize contact image thumbnails

I noticed that when uploading a user photo, CiviCRM is returning the full-size image and relying on the browser to resize it to a thumbnail.

The first patch allows the use of the Drupal image_resize() function if it is available.

The second patch corrects CRM_Contact_BAO_Contact::getThumbSize() so that the returned width is an integer rather than a float.