Investigate better ways to access a Membase backend

[jkoshy]

The code currently accesses membase in memcache compatibility mode. This is sub-optimal in a couple of ways:

• Traffic to the membase is routed through a proxy (moxi), which implies an additional hop for data to traverse.
• The python client used by the current server does not deal with all the error responses that a membase server could issue.
• The memcache protocol itself has limits that the membase does not have.

Choose and use a suitable interface library so that a Membase backend can be accessed efficiently.