Rephrase Arc documentation changes regarding clones

Make it clearer that `Arc::clone()` in fact creates a whole new
Arc with the internal pointer pointing to the same location as
the source Arc.

Author: rask

src/liballoc/sync.rs

@@ -49,8 +49,9 @@ const MAX_REFCOUNT: usize = (isize::MAX) as usize;
 ///
 /// The type `Arc<T>` provides shared ownership of a value of type `T`,
 /// allocated in the heap. Invoking [`clone`][clone] on `Arc` produces
-/// a new pointer to the same `Arc` reference value in the heap. When the last
-/// `Arc` pointer to a given value is destroyed, the pointed-to value is also
+/// a new `Arc` instance, which points to the same value on the heap as the
+/// source `Arc`, while increasing a reference count. When the last `Arc`
+/// pointer to a given value is destroyed, the pointed-to value is also
 /// destroyed.
 ///
 /// Shared references in Rust disallow mutation by default, and `Arc` is no
@@ -107,8 +108,7 @@ const MAX_REFCOUNT: usize = (isize::MAX) as usize;
 /// // The two syntaxes below are equivalent.
 /// let a = foo.clone();
 /// let b = Arc::clone(&foo);
-/// // a and b both point to the same memory location where foo resides
-/// // (not where the value wrapped by foo resides).
+/// // a and b both point to the same memory location as foo
 /// ```
 ///
 /// The [`Arc::clone(&from)`] syntax is the most idiomatic because it conveys more explicitly