[cleanup] Make initialization consistent for all make_array implementations

While the following is legal c++11

  array<T,n> foo = { t1, t2, ...}

older compilers (namely gcc-4.4) issue a warning on missing braces.

dune/common/array.hh

@@ -116,7 +116,7 @@ namespace Dune
                           const T &t4, const T &t5, const T &t6, const T &t7,
                           const T &t8, const T &t9)
   {
-    array<T, 10> result = { t0, t1, t2, t3, t4, t5, t6, t7, t8, t9 };
+    array<T, 10> result = { {t0, t1, t2, t3, t4, t5, t6, t7, t8, t9} };
     return result;
   }