Memcached StorageService

[Marvin Addison]

> I guess it depends what scenario would be affected by the performance hit,
> but like I said, the straight update() call definitely doesn't need to
> return it, I can change that.

Ok, I think we may have a compromise:

- Change update() methods to return boolean
- Keep updateWithVersion() unchanged

I can do the extra read to get the version in the updateWithVersion
case, but since it's not the common case in the IdP
(StorageBackedIdPSession) it presumably won't have a dramatic impact.

> I can't think of a good name for updateWithVersionReturnBoolean,
> plus the method proliferation is a bit nuts already.

I think we can and should try to avoid method bloat. The API is clean
and complete as-is.

Thanks for working with me on this.

Best,
M