Fix the links in Vec(Deque)-from-Vec(Deque)

Ok, I can't use `std` in doc-links, only in doc-tests.  Try 7...

src/liballoc/collections/vec_deque.rs

@@ -2711,6 +2711,9 @@ impl<T: fmt::Debug> fmt::Debug for VecDeque<T> {
 impl<T> From<Vec<T>> for VecDeque<T> {
     /// Turn a [`Vec<T>`] into a [`VecDeque<T>`].
     ///
+    /// [`Vec<T>`]: crate::vec::Vec
+    /// [`VecDeque<T>`]: crate::collections::VecDeque
+    ///
     /// This avoids reallocating where possible, but the conditions for that are
     /// strict, and subject to change, and so shouldn't be relied upon unless the
     /// `Vec<T>` came from `From<VecDeque<T>>` and hasn't been reallocated.
@@ -2742,6 +2745,9 @@ impl<T> From<Vec<T>> for VecDeque<T> {
 impl<T> From<VecDeque<T>> for Vec<T> {
     /// Turn a [`VecDeque<T>`] into a [`Vec<T>`].
     ///
+    /// [`Vec<T>`]: crate::vec::Vec
+    /// [`VecDeque<T>`]: crate::collections::VecDeque
+    ///
     /// This never needs to re-allocate, but does need to do O(n) data movement if
     /// the circular buffer doesn't happen to be at the beginning of the allocation.
     ///