Auto merge of #23333 - oli-obk:slice_from_raw_parts, r=alexcrichton

at least that's what the docs say: http://doc.rust-lang.org/std/slice/fn.from_raw_parts.html

A few situations got prettier. In some situations the mutability of the resulting and source pointers differed (and was cast away by transmute), the mutability matches now.

src/libstd/old_io/mod.rs

@@ -931,15 +931,15 @@ impl<'a> Reader for &'a mut (Reader+'a) {
 // Private function here because we aren't sure if we want to expose this as
 // API yet. If so, it should be a method on Vec.
 unsafe fn slice_vec_capacity<'a, T>(v: &'a mut Vec<T>, start: uint, end: uint) -> &'a mut [T] {
-    use raw::Slice;
+    use slice;
     use ptr::PtrExt;
 
     assert!(start <= end);
     assert!(end <= v.capacity());
-    transmute(Slice {
-        data: v.as_ptr().offset(start as int),
-        len: end - start
-    })
+    slice::from_raw_parts_mut(
+        v.as_mut_ptr().offset(start as int),
+        end - start
+    )
 }
 
 /// A `RefReader` is a struct implementing `Reader` which contains a reference