Rename std::ptr::Shared to NonNull

`Shared` is now a deprecated `type` alias.

CC https://github.com/rust-lang/rust/issues/27730#issuecomment-352800629

src/liballoc/vec.rs

@@ -78,7 +78,7 @@ use core::num::Float;
 use core::ops::{InPlace, Index, IndexMut, Place, Placer};
 use core::ops;
 use core::ptr;
-use core::ptr::Shared;
+use core::ptr::NonNull;
 use core::slice;
 
 use borrow::ToOwned;
@@ -1124,7 +1124,7 @@ impl<T> Vec<T> {
                 tail_start: end,
                 tail_len: len - end,
                 iter: range_slice.iter(),
-                vec: Shared::from(self),
+                vec: NonNull::from(self),
             }
         }
     }
@@ -1745,7 +1745,7 @@ impl<T> IntoIterator for Vec<T> {
             let cap = self.buf.cap();
             mem::forget(self);
             IntoIter {
-                buf: Shared::new_unchecked(begin),
+                buf: NonNull::new_unchecked(begin),
                 phantom: PhantomData,
                 cap,
                 ptr: begin,
@@ -2267,7 +2267,7 @@ impl<'a, T> FromIterator<T> for Cow<'a, [T]> where T: Clone {
 /// [`IntoIterator`]: ../../std/iter/trait.IntoIterator.html
 #[stable(feature = "rust1", since = "1.0.0")]
 pub struct IntoIter<T> {
-    buf: Shared<T>,
+    buf: NonNull<T>,
     phantom: PhantomData<T>,
     cap: usize,
     ptr: *const T,
@@ -2442,7 +2442,7 @@ pub struct Drain<'a, T: 'a> {
     tail_len: usize,
     /// Current remaining range to remove
     iter: slice::Iter<'a, T>,
-    vec: Shared<Vec<T>>,
+    vec: NonNull<Vec<T>>,
 }
 
 #[stable(feature = "collection_debug", since = "1.17.0")]