Add AddressMemcachedSessionComparator

[ssup2]

Memecached cluster servers/client in container cluster such as k8s has the following characteristics.

• Servers can be added or deleted at any time.
• For client (App, Service) loadbalancing, the same client runs in the multiple containers.
• To increase the client cache hit, it is recommended to use the same key/server Map.

Now xmemcached only supports index-based sorting of servers. Index-based sorting can not guarantee the same key/server map that works in multiple containers. To resolve the this issue, I added an address-based sorting method.

The modifications and additions are as follows.

• Rename MemcachedSessionComparator to IndexMemcachedSessionComparator
• Add MemcachedSessionComparator Interface
• Add AddressMemcachedSessionComparator

[ssup2]

is there no feedback??