lib,src: add unix socket getsockname/getpeername
The implementation is a minor API change in that socket.address() now
returns a { address: '/path/to/socket' }
object, like it does for TCP
and UDP sockets. Before this commit, it returned socket._pipeName
,
which is a string when present.
Fixes: iojs#954
R=@trevnorris?
https://jenkins-iojs.nodesource.com/job/iojs+any-pr+multi/195/