Support Direct Gets by subject

[codegangsta]

This PR brings in client support for nats-io/nats-server#3325, which adds server support for direct gets by a particular subject. This should now allow direct gets to work with KVs properly

[kozlovic]

@codegangsta Also, unrelated to your PR, but since you updated the server version, and due to @bruth recent change in the server, this test fails:

=== RUN   TestJetStreamManagement/update_consumer
    js_test.go:1417: Error on update: max waiting can not be updated

would need to be updated in order for the Travis CI to pass. Could you do it?

[codegangsta]

Sure I'll take a look

[kozlovic]

Meaning that server does not support it, so the test should not try to modify or at least not expect it to be updated :-)

[coveralls]

Coverage decreased (-0.005%) to 85.721% when pulling e7a08b8 on JMS-DirectGetLastBySubject into 59d7d9c on main.

[codegangsta]

@kozlovic looks like this may be a flaky test?

=== RUN   TestHotSpotReconnect
    cluster_test.go:341: Connected clients to server: nats://127.0.0.1:1226 out of range: 23

I'll run it again

[codegangsta]

@kozlovic all passed!

[kozlovic]

LGTM