impl FusedIterator for IpSubnets and related

src/ipnet.rs

@@ -3,6 +3,7 @@ use std::cmp::Ordering::{Less, Equal};
 use std::convert::From;
 use std::error::Error;
 use std::fmt;
+use std::iter::FusedIterator;
 use std::net::{IpAddr, Ipv4Addr, Ipv6Addr};
 use std::option::Option::{Some, None};
 
@@ -1445,6 +1446,10 @@ impl Iterator for Ipv6Subnets {
     }
 }
 
+impl FusedIterator for IpSubnets {}
+impl FusedIterator for Ipv4Subnets {}
+impl FusedIterator for Ipv6Subnets {}
+
 // Generic function for merging a vector of intervals.
 fn merge_intervals<T: Copy + Ord>(mut intervals: Vec<(T, T)>) -> Vec<(T, T)> {
     if intervals.len() == 0 {