Support EC2 ELB cross-zone load balancing

Allow for EC2 ELB Load Balancers to use the new cross-zone load balancing
feature which better distributes load across all Availability Zones.

http://aws.amazon.com/about-aws/whats-new/2013/11/06/elastic-load-balancing-adds-cross-zone-load-balancing/

Disabled by default unless you add "cross_zone_loadbalancing true" to your ELB definition.
fog errors look different in fog 1.19.0, now they look like "ERROR: Fog::Compute::AWS::Error: Duplicate => The permission \'1500008810-1-1-65535\' has already been authorized on the specified group"