auto merge of #12348 : brunoabinader/rust/libcollections-list-refactory, r=alexcrichton

This PR includes:
- Create an iterator for ```List<T>``` called ```Items<T>```;
- Move all list operations inside ```List<T>``` impl;
- Removed functions that are already provided by ```Iterator``` trait;
- Refactor on ```len()``` and ```is_empty``` using ```Container``` trait;
- Bunch of minor fixes;

A replacement for using @ is intended, but still in discussion.

Closes #12344.

src/test/run-pass/log-knows-the-names-of-variants-in-std.rs

@@ -11,7 +11,7 @@
 // except according to those terms.
 
 extern crate collections;
-use collections::list;
+use collections::list::List;
 
 #[deriving(Clone)]
 enum foo {
@@ -24,8 +24,8 @@ fn check_log<T>(exp: ~str, v: T) {
 }
 
 pub fn main() {
-    let x = list::from_vec([a(22u), b(~"hi")]);
-    let exp = ~"@Cons(a(22u), @Cons(b(~\"hi\"), @Nil))";
+    let x = List::from_vec([a(22u), b(~"hi")]);
+    let exp = ~"Cons(a(22u), @Cons(b(~\"hi\"), @Nil))";
     let act = format!("{:?}", x);
     assert!(act == exp);
     check_log(exp, x);

src/test/run-pass/non-boolean-pure-fns.rs

@@ -14,19 +14,19 @@
 
 extern crate collections;
 
-use collections::list::{List, Cons, Nil, head, is_empty};
+use collections::list::{List, Cons, Nil};
 
-fn pure_length_go<T:Clone>(ls: @List<T>, acc: uint) -> uint {
+fn pure_length_go<T>(ls: @List<T>, acc: uint) -> uint {
     match *ls { Nil => { acc } Cons(_, tl) => { pure_length_go(tl, acc + 1u) } }
 }
 
-fn pure_length<T:Clone>(ls: @List<T>) -> uint { pure_length_go(ls, 0u) }
+fn pure_length<T>(ls: @List<T>) -> uint { pure_length_go(ls, 0u) }
 
-fn nonempty_list<T:Clone>(ls: @List<T>) -> bool { pure_length(ls) > 0u }
+fn nonempty_list<T>(ls: @List<T>) -> bool { pure_length(ls) > 0u }
 
 fn safe_head<T:Clone>(ls: @List<T>) -> T {
-    assert!(!is_empty(ls));
-    return head(ls);
+    assert!(!ls.is_empty());
+    return ls.head().unwrap().clone();
 }
 
 pub fn main() {