Checking curve support fails in 0.10.0

[glennpierce]

I have code like

if !zmq::has("curve").expect("some always expected") {
        panic!("Zeromq curve support required");
}   

In version = "0.9.2" this works fine. If I update to version = "0.10.0" the panic is called.

do I need todo something else for 0.10.0 ?

[glennpierce]

Duplicate of #357