De-mode vec::each() and many of the str iteration routines

Note that the method foo.each() is not de-moded, nor the other
vec routines.

src/test/compile-fail/borrowck-mut-vec-as-imm-slice-bad.rs

@@ -1,6 +1,6 @@
 fn want_slice(v: &[int]) -> int {
     let mut sum = 0;
-    for vec::each(v) |i| { sum += i; }
+    for vec::each(v) |i| { sum += *i; }
     return sum;
 }
 

src/test/compile-fail/issue-2151.rs

@@ -1,5 +1,5 @@
 fn main() {
-    do vec::iter(fail) |i| {
+    for vec::each(fail) |i| {
         log (debug, i * 2);
         //~^ ERROR the type of this value must be known
    };

src/test/compile-fail/liveness-issue-2163.rs

@@ -1,5 +1,6 @@
 fn main() {
     let a: ~[int] = ~[];
-    vec::each(a, fn@(_x: int) -> bool { //~ ERROR not all control paths return a value
+    vec::each(a, fn@(_x: &int) -> bool {
+        //~^ ERROR not all control paths return a value
     });
 }

src/test/compile-fail/vec-concat-bug.rs

@@ -2,9 +2,9 @@ fn concat<T: Copy>(v: ~[const ~[const T]]) -> ~[T] {
     let mut r = ~[];
 
     // Earlier versions of our type checker accepted this:
-    vec::iter(v, |&&inner: ~[T]| {
+    vec::each(v, |inner: &~[T]| {
         //~^ ERROR values differ in mutability
-        r += inner;
+        r += *inner; true
     });
 
     return r;