add max value from iterator

Author: matthew-piziak

Diff for: src/test/run-pass/iter-step-overflow-debug.rs

@@ -15,12 +15,14 @@ use std::panic;
 fn main() {
     let r = panic::catch_unwind(|| {
         let mut it = u8::max_value()..;
+        it.next().unwrap(); // 255
         it.next().unwrap();
     });
     assert!(r.is_err());
 
     let r = panic::catch_unwind(|| {
         let mut it = i8::max_value()..;
+        it.next().unwrap(); // 127
         it.next().unwrap();
     });
     assert!(r.is_err());

Diff for: src/test/run-pass/iter-step-overflow-ndebug.rs

@@ -12,8 +12,10 @@
 
 fn main() {
     let mut it = u8::max_value()..;
+    assert_eq!(it.next().unwrap(), 255);
     assert_eq!(it.next().unwrap(), u8::min_value());
 
     let mut it = i8::max_value()..;
+    assert_eq!(it.next().unwrap(), 127);
     assert_eq!(it.next().unwrap(), i8::min_value());
 }