Upcoming Rust (>0.6) does not support 'extern mod <ident> { }' anymore.
Rename str/vec::from_slice to str/vec::to_owned. See Rust issue #3356
Remove deprecated `ptr::addr_of'. See: https://github.com/mozilla/rust/pull/6011
Merge pull request #7 from smvv/master

Make zmq compatible with upcoming Rust version (>0.6)