Rollup merge of rust-lang#23263 - alexcrichton:stabilize-from-raw-parts, r=brson

 These new APIs have had some time to bake now, and no pressing issues have come
up so they should be ok for stabilizing. Specifically, these two APIs were
stabilized:

* `slice::from_raw_parts`
* `slice::from_raw_parts_mut`

Author: Manishearth

src/libcore/slice.rs

@@ -1446,7 +1446,7 @@ pub fn mut_ref_slice<'a, A>(s: &'a mut A) -> &'a mut [A] {
 /// }
 /// ```
 #[inline]
-#[unstable(feature = "core")]
+#[stable(feature = "rust1", since = "1.0.0")]
 pub unsafe fn from_raw_parts<'a, T>(p: *const T, len: usize) -> &'a [T] {
     transmute(RawSlice { data: p, len: len })
 }
@@ -1458,7 +1458,7 @@ pub unsafe fn from_raw_parts<'a, T>(p: *const T, len: usize) -> &'a [T] {
 /// as not being able to provide a non-aliasing guarantee of the returned
 /// mutable slice.
 #[inline]
-#[unstable(feature = "core")]
+#[stable(feature = "rust1", since = "1.0.0")]
 pub unsafe fn from_raw_parts_mut<'a, T>(p: *mut T, len: usize) -> &'a mut [T] {
     transmute(RawSlice { data: p, len: len })
 }