Localization of WPeC vars is not more explicit

* The loop that was taking the localized admin js vars out of the localization structure and putting them into the window content has been replaced by explicit assignments.  Although it is a little more code than the prior loop it should now be easier to see what is happening.
* For localized js vars added after 3.8.14 three utility functions have been provided to access localized vars

```
 wpsc_admin_var_get ( name )
 wpsc_admin_var_set ( name, value )
 wpsc_admin_var_isset ( name, value );
```

**Also...**
Updated an incomplete comment related to the WPeC visitor cookie


This is the admin side of the audit required to close issue #1110