vec::slice is faster now (Issue #2719)

src/libcore/vec.rs

@@ -255,18 +255,14 @@ fn from_mut<T>(+v: [mut T]) -> [T] {
     assert (start <= end);
     assert (end <= len(v));
     let mut result = [];
-
-//    unchecked {
-//        push_all(result, view(v, start, end));
-//    }
-
-    let mut i = start;
-    while i < end { result += [v[i]]; i += 1u; }
+    unchecked {
+        push_all(result, view(v, start, end));
+    }
     ret result;
 }
 
 #[doc = "Return a slice that points into another slice."]
-pure fn view<T: copy>(v: [const T]/&a, start: uint, end: uint) -> [T]/&a {
+pure fn view<T: copy>(v: [const T]/&, start: uint, end: uint) -> [T]/&a {
     assert (start <= end);
     assert (end <= len(v));
     unpack_slice(v) {|p, _len|