Cleanup. Changed HashMap's internal layout.

* use of NonZero hashes
* refactoring
* correct explanation of the load factor
* better nomenclature
* 'probe distance' -> 'displacement'

src/libstd/collections/hash/bench.rs

@@ -55,6 +55,24 @@ fn grow_by_insertion(b: &mut Bencher) {
     });
 }
 
+#[bench]
+fn grow_by_insertion_large(b: &mut Bencher) {
+    use super::map::HashMap;
+
+    let mut m = HashMap::new();
+
+    for i in range_inclusive(1, 1000) {
+        m.insert(i, (String::new(), String::new()));
+    }
+
+    let mut k = 1001;
+
+    b.iter(|| {
+        m.insert(k, (String::new(), String::new()));
+        k += 1;
+    });
+}
+
 #[bench]
 fn find_existing(b: &mut Bencher) {
     use super::map::HashMap;