Touch with expiry time 0 does not work

According to the specification touch 0 should set the expiry time to never expire, but for couchbase buckets it cause the document to expire immediately (memcached buckets does the right thing here).

Easy test is:
telnet localhost 11211
add a 1 30 1
a
touch a 0
get a

On a couchbase bucket you won't get anything back from the last get, whereas on memcached buckets you'll get the document a.

The bug is caused by the following code in ep_engine.cc (in EventuallyPersistentEngine::touch):

exptime = serverApi->core->abstime(serverApi->core->realtime(exptime));

Instead the code should be:

    if (exptime != 0) {
        exptime = serverApi->core->abstime(serverApi->core->realtime(exptime));
    }