Add an option to alter optionset in flexslider_add

In the latest dev release, as well as the alpha release, there is a comment stating: "@todo add alter hook for optionset". As I need to add a dynamically created unique ID as a "Sync" option, I needed this alter hook. So I took the liberty of creating a small patch, implementing

drupal_alter('flexslider_optionset', $optionset);

I added the code as a patch as well. The patch was made using the current stable alpha release.