[set] Fix set copy/move constructors to actually work

Ouch!

src/hb-set.hh

diff --git a/src/hb-set.hh b/src/hb-set.hh
index 5840a1a..c9725e8 100644
--- a/src/hb-set.hh
+++ b/src/hb-set.hh
@@ -44,7 +44,7 @@
   hb_sparseset_t (const hb_sparseset_t& other) : hb_sparseset_t () { set (other); }
   hb_sparseset_t (hb_sparseset_t&& other) : hb_sparseset_t () { s = std::move (other.s); }
   hb_sparseset_t& operator= (const hb_sparseset_t& other) { set (other); return *this; }
-  hb_sparseset_t& operator= (hb_sparseset_t&& other) { s =  std::move (other.s); return *this; }
+  hb_sparseset_t& operator= (hb_sparseset_t&& other) { s = std::move (other.s); return *this; }
   friend void swap (hb_sparseset_t& a, hb_sparseset_t& b) { hb_swap (a.s, b.s); }
 
   hb_sparseset_t (std::initializer_list<hb_codepoint_t> lst) : hb_sparseset_t ()
@@ -158,15 +158,19 @@
 
 struct hb_set_t : hb_sparseset_t<hb_bit_set_invertible_t>
 {
-  hb_set_t () = default;
+  using sparseset = hb_sparseset_t<hb_bit_set_invertible_t>;
+
   ~hb_set_t () = default;
-  hb_set_t (hb_set_t&) = default;
+  hb_set_t () : sparseset () {};
+  hb_set_t (const hb_set_t &o) : sparseset ((sparseset &) o) {};
+  hb_set_t (hb_set_t&& o) : sparseset (std::move ((sparseset &) o)) {}
   hb_set_t& operator= (const hb_set_t&) = default;
   hb_set_t& operator= (hb_set_t&&) = default;
-  hb_set_t (std::initializer_list<hb_codepoint_t> lst) : hb_sparseset_t<hb_bit_set_invertible_t> (lst) {}
+  hb_set_t (std::initializer_list<hb_codepoint_t> lst) : sparseset (lst) {}
   template <typename Iterable,
-	    hb_requires (hb_is_iterable (Iterable))>
-  hb_set_t (const Iterable &o) : hb_sparseset_t<hb_bit_set_invertible_t> (o) {}
+	    hb_requires (hb_is_iterable (Iterable) &&
+			 !hb_is_same (hb_decay<Iterable>, hb_set_t))>
+  hb_set_t (const Iterable &o) : sparseset (o) {}
 };
 
 static_assert (hb_set_t::INVALID == HB_SET_VALUE_INVALID, "");

src/test-set.cc

diff --git a/src/test-set.cc b/src/test-set.cc
index 286f1a9..e28d7e6 100644
--- a/src/test-set.cc
+++ b/src/test-set.cc
@@ -42,21 +42,24 @@
   /* Test copy assignment. */
   {
     hb_set_t v1 {1, 2};
-    hb_set_t v2 = v1;
+    hb_set_t v2;
+    v2 = v1;
     assert (v1.get_population () == 2);
     assert (v2.get_population () == 2);
   }
 
   /* Test move constructor. */
   {
-    hb_set_t v {hb_set_t {1, 2}};
+    hb_set_t v (hb_set_t {1, 2});
     assert (v.get_population () == 2);
   }
 
   /* Test move assignment. */
   {
+    hb_set_t s = hb_set_t {1, 2};
     hb_set_t v;
-    v = hb_set_t {1, 2};
+    v = std::move (s);
+    assert (s.get_population () == 0);
     assert (v.get_population () == 2);
   }
 
@@ -67,9 +70,15 @@
     s.add (18);
     s.add (12);
 
-    hb_set_t v (s);
+    hb_vector_t<hb_codepoint_t> v (s);
+    hb_set_t v0 (v);
+    hb_set_t v1 (s);
+    hb_set_t v2 (std::move (s));
 
-    assert (v.get_population () == 2);
+    assert (s.get_population () == 0);
+    assert (v0.get_population () == 2);
+    assert (v1.get_population () == 2);
+    assert (v2.get_population () == 2);
   }
 
   /* Test initializing from iterator. */