wpsc_add_cookie called on init causes corruption

[donnchawp]

Thank you for using wpsc_add_cookie()! Unfortunately it's causing problems because it's being called on init. Multiple processes on websites using WP Super Cache try to update the plugin configuration file which causes the file to be corrupted as writes happen so often. We're going to address this issue in WP Super Cache but until then it's still a problem.

It could probably be avoided by using admin_init rather than the init action, but the cookies should really only be updated on the settings page for this plugin.