support DATA-PRESENT in the p2p protocol proxy

support DATA-PRESENT in the p2p protocol proxy

But not yet when proxying to special remotes.

When proxying for a cluster, the client can store the object on any node
or nodes of the cluster, and send DATA-PRESENT. That gets proxied to each
node, and if any of them agree that they have the data, the proxy will
respond with SUCCESS or SUCCESS-PLUS.

I think it's ok to not check for the proxied remotes supporting protocol
version 4. When there are multiple remotes in a cluster, it behaves as
described above, and if they all respond with ERROR, the result will be
FAILURE. And when not proxying for a cluster, the proxy negotiates the
p2p protocol to be the same version or lower than the proxied remote,
which will prevent sending DATA-PRESENT when it's too old.