Setting a non-existant key from VBucketAwareCouchbaseClient throws an exception instead of returning None

The docs don't match the code. We need to determine which one is correct (or which route we'd prefer taking), write some tests, and make the docs and code match.

Reported via http://disq.us/78w7hy?imp=7fd22085-2821-40da-9b3f-0e5134554a91&thread=574422822&zone=email_notification&event=shortener_click
Using couchbase-python-client v0.6.0 from the MB 2.0 DP SDK downloads, the above doesn't seem to be true. I am seeing the following exception thrown (instead of None being returned) when trying to get a non-existant key from a VBucketAwareCouchbaseClient:

couchbase.couchbaseclient.MemcachedError: Memcached error #1: Not found

Also, the get function doesn't return object but a tuple, with the object is in position 2.