[iter] Make hb_sorted_array_t work as iter

Ugly, but does the job.

src/hb-array.hh

diff --git a/src/hb-array.hh b/src/hb-array.hh
index 52b775e..7dd02cd 100644
--- a/src/hb-array.hh
+++ b/src/hb-array.hh
@@ -194,9 +194,11 @@
 template <typename Type>
 struct hb_sorted_array_t :
 	hb_sorted_iter_t<hb_sorted_array_t<Type>, Type>,
-	hb_array_t<Type>,
-	hb_iter_mixin_t<hb_sorted_array_t<Type>, Type>
+	hb_array_t<Type>
 {
+  typedef hb_sorted_iter_t<hb_sorted_array_t<Type>, Type> iter_base_t;
+  HB_ITER_USING (iter_base_t);
+
   hb_sorted_array_t () : hb_array_t<Type> () {}
   hb_sorted_array_t (const hb_array_t<Type> &o) : hb_array_t<Type> (o) {}
   hb_sorted_array_t (Type *array_, unsigned int length_) : hb_array_t<Type> (array_, length_) {}