std: Reexport std::net::tcp::Incoming

This iterator was mistakenly not reexported at the top level, preventing
actually naming the type!

Closes rust-lang#25519

src/libstd/net/mod.rs

@@ -19,7 +19,7 @@ use sys_common::net as net_imp;
 
 pub use self::ip::{IpAddr, Ipv4Addr, Ipv6Addr, Ipv6MulticastScope};
 pub use self::addr::{SocketAddr, SocketAddrV4, SocketAddrV6, ToSocketAddrs};
-pub use self::tcp::{TcpStream, TcpListener};
+pub use self::tcp::{TcpStream, TcpListener, Incoming};
 pub use self::udp::UdpSocket;
 pub use self::parser::AddrParseError;