Correct handling of operation timeouts.

Currently, a kv operation that times out raises a client_exception with a lcb error code of 201. That is interpreted as a FAIL_EXPIRY. That's wrong – that should only happen when the transaction itself expires. We need to add an attempt_expired exception, derived from client_error, and classify that properly (and use it in the hooks, etc..).

We need to add kv timeout to the transaction_config as well. Check on other inconsistencies while we are there. Speaking of kv timeouts... Java has durable vs non-durable timeouts, and uses them in the mutating operation's options when a kv timeout isn't specified in the transaction options. Consider adding this to the client, using in txns.