Add support for Ban Lurker compatible bans to Varnish module

Please see: https://www.varnish-software.com/blog/ban-lurker
Please see: http://kristianlyng.wordpress.com/2010/07/28/smart-bans-with-varnish/

The current ban method uses req.host and req.url on sites with lower traffic to pages bans can be able to stay in the system especially when used with the expire module with expiring taxonomy and referring pages each new post, delete, etc can cause a new ban to be listed in Varnish. Each ban can not expire until every page in the cache has been looked up. In the case of req.url/req.host this means a end user must visit the page before it can be expired from the cache.

The patch attached adds a new option to the admin interface to allow choosing normal req.host/req.url or instead use obj.http.x-host/obj.http.x-url which is Ban Lurker comptatible.

Please note this is my first Drupal project patch so I apologies if anything in the patch is out of spec to standards.

No simpletest items were added I am not sure if this is the sort of thing that needs a test or not?

I called the Ban types: “Normal” and “Ban Lurker” I am open to different names. Possible other names options could be “req.http.host/req.http.url" and "obj.http.x-host/obj.http.x-url" (this also opens the possibility of a different patch that removes host all together for sites that don't normalize their hostnames but that is a different discussion)

VCL mods are needed if you use the Ban Lurker.

sub vcl_fetch {
set obj.http.x-host = req.host;
set obj.http.x-url = req.url;
}
sub vcl_deliver {
unset resp.http.x-host; # Optional
unset resp.http.x-url; # Optional
}

Note: So long as VCL mods are done user can use x-url x-host based bans even if they do not use Ban Lurker.