Allow purging of additional basepaths

If this module is used on a Domain Access-enabled site, or on a site with multiple domains configured in some other way, there's a good possibility that one path might be accessible through multiple domains.

Currently, only the domain that's actively being used when, for example, hook_node_update() is hit is cleared.

So if you have:

• www.example.com
• another.example.com

And the content editor is logged in at www.example.com, only www.example.com/path would be cleared.

Modules like Acquia Purge have configuration variables like acquia_purge_domains to allow for multiple domains to be configured explicitly, and supporting this kind of functionality doesn't seem like it would be too difficult to do, likely only involving a few changes in AkamaiCacheControlClient to make basepath able to be an array of base paths.