Memcached StorageService

[Marvin Addison]

> I'm fine with that. I just changed the int to a long, I'll patch the
> update methods now.

I got everything working to my satisfaction except
updateContextExpiration, which simply isn't possible with this
implementation. I saw that at least one other StorageService did not
implement that method, so I figured it was ok. If anyone has some
spare cycles I would appreciate review:

https://github.com/serac/idp-memcached-storage

I will be incorporating this component into our dev environment in the
next couple weeks, so it will get some live testing. The primary use
case for this component is supporting protocols that need to access
IdP session state over back-channel protocols (CAS in our case) in a
HA environment. Memcached has proven for us a preferable alternative
to a database backend in terms of performance, simplicity, and
availability, so I'm looking forward to putting this component through
the paces.

I'm interested in contributing this to the project. It only pulls in
one additional dependency, net.spy:spymemcached [1], which seems
relatively innocuous. I'd appreciate feedback on contributing.

Best,
M

[1] https://repo1.maven.org/maven2/net/spy/spymemcached/2.11.4/spymemcached-2.11.4.pom