Deprecate "addUser" helpers in favor of "createUser" and "updateUser" helpers

In the server, user creation is done through the command "createUser". There is a shell helper "addUser" that has been around for a while, but is being deprecated in 2.6 according to SERVER-11555, in favor of a new shell helper "createUser".

In the past we have been inconsistent in the verbs we use for creation events. We had the addUser helper, but have createCollection, createDatabase, and createIndex operations. Also, in other databases, the term "create" is much more heavily used than the term "add". It has been pointed out to me by andreas.nilsson@10gen.com that having so many different verbs can be confusing to non-native english speakers.

We should standardize our terminology around the verb "create" rather than "add" so that we have consistent and predictable naming.

Since we have already gone ahead and done this in the server, we should do this in the drivers as well so that no matter what tool you are using to connect to MongoDB, you know that users are created via a createUser call, you shouldn't have to use addUser in some places and createUser in others, and be expected to keep track of when you use which.