Merge branch '0.4' of https://github.com/bluss/arrayvec into merge-0.4

* '0.4' of https://github.com/bluss/arrayvec:
  0.4.9
  TEST: Add test that ensures the MaybeUninit impl is used on nightly
  FIX: Remove use of uninitialized in ArrayString
  FEAT: Implement a "MaybeUninit" and use it conditionally
  TEST: Add test that Some(ArrayVec<[&_;_]>).is_some()
  MAINT: Test the 0.4 branch in travis

tests/tests.rs

@@ -281,6 +281,14 @@ fn test_compact_size() {
     assert!(mem::size_of::<QuadArray>() <= 24);
 }
 
+#[test]
+fn test_still_works_with_option_arrayvec() {
+    type RefArray = ArrayVec<[&'static i32; 2]>;
+    let array = Some(RefArray::new());
+    assert!(array.is_some());
+    println!("{:?}", array);
+}
+
 #[test]
 fn test_drain() {
     let mut v = ArrayVec::from([0; 8]);
@@ -617,3 +625,12 @@ fn test_sizes_129_255() {
     ArrayVec::from([0u8; 255]);
 }
 
+
+#[test]
+fn test_nightly_uses_maybe_uninit() {
+    if option_env!("ARRAYVECTEST_ENSURE_UNION").map(|s| !s.is_empty()).unwrap_or(false) {
+        assert!(cfg!(has_manually_drop_in_union));
+        type ByteArray = ArrayVec<[u8; 4]>;
+        assert!(mem::size_of::<ByteArray>() == 5);
+    }
+}