rename std::iterator to std::iter

The trait will keep the `Iterator` naming, but a more concise module
name makes using the free functions less verbose. The module will define
iterables in addition to iterators, as it deals with iteration in
general.

src/libstd/path.rs

@@ -21,7 +21,7 @@ use c_str;
 use clone::Clone;
 use cmp::Eq;
 use container::Container;
-use iterator::{Iterator, range};
+use iter::{Iterator, range};
 use libc;
 use num;
 use option::{None, Option, Some};