Memcache admin incompatible with Twemproxy

Problem/Motivation

When load balancing memcache behind a proxy such as Twemproxy, the Memcache Admin module gives the false impression that memcache is non-functional. The issue is that the Memcache Admin module uses the `stats` command to get necessary statistics to display info. This command is not available in twemproxy (https://github.com/twitter/twemproxy/blob/master/notes/memcache.md).

Steps to reproduce

Configure a single Memcache and Twemproxy instance.
Validate functionality using telnet to set and get values via the proxy.
Configure a Drupal site to use the Twemproxy instance.
Telnet into the memcache instance and use `stats items` to list all items, and `stats cachedump keyNumber numberOfValuesToShow` to get particular cache entries to validate Drupal is using memcache.
Enable the Memcache Admin module.
View the Memcache Admin report.

Proposed resolution

Easiest: Update Readme, or error message to inform the user that such an error is normal if Memcache is behind a proxy such as Twemproxy.

Harder: Allow for a Memcache Admin specific server override to get memcache statistics from the underlying memcache instances bypassing Twemproxy, but only for the purpose of stats display.

Remaining tasks

Create patch.

User interface changes

Depends on approach.

API changes

None.

Data model changes

None.