With new version of rust (1.10) it's now possible to use UnixListener and UnixStream from stdlib.
This patch allows to disable dependency on external crate.
Using external crate is enabled by default to preserve compatibility.
Coverage remained the same at 100.0% when pulling c81cc4bf489dc03048f4556426b9fe4f4b25ae29 on mkocot:unix-socket-from-stdlib into a00dca54b64ea75897b1623b4bd83fa979127ac7 on softprops:master.
With new version of rust (1.10) it's now possible to use UnixListener and UnixStream from stdlib. This patch allows to disable dependency on external crate. Using external crate is enabled by default to preserve compatibility.