[shy-1234]

What

Changes to EVCacheMemcachedClient.mutate (incr/decr):

• When the mutate times out: it calls op.timeOut() and MemcachedConnection.opTimedOut(op), then returns -1. The ipc.client.call timer is tagged ipc.result=failure, ipc.status=timeout and evc.failed.host.
• When the node answers with any status except timed out or cancelled: it calls MemcachedConnection.opSucceeded(op).

Why

• No timeout metric: a timed-out mutate records its timer with no ipc.status or ipc.result tag, so mutate timeouts don't show up in metrics.
• Timeouts not counted: mutate timeouts never add to the node's continuous-timeout counter.
• Late writes: an op that times out while still queued can be sent, and applied, after the caller already got -1. Calling op.timeOut() makes the IO thread drop it.
• Counter not reset: mutate answers never reset the counter, so on clients that mostly incr/decr it stops counting only consecutive timeouts.

The latch alone decides whether the mutate timed out, so a reply that arrives after the deadline can't change the result. The status holder is now an AtomicReference, because op.timeOut() runs the callback on the caller thread while the IO thread may run it too.

Testing

EVCacheMemcachedClientMutateTest has 6 tests and is added to test-suite.xml. It runs a real client against a fake memcached on 127.0.0.1 and covers:

• a silent server: timeout timer tags and counter increment;
• the counter counting 1, 2, 3 and then resetting on an answer;
• an error answer resetting the counter;
• a cancelled op leaving the counter unchanged;
• a timed-out op that was never sent not reaching the server after reconnect;
• an answered mutate returning the server's value.