[libsigcplusplus] test_accum_iter: Use of decltype(auto).

[Murray Cumming <murrayc src gnome org>]

commit 999b9050964bb00ba1f72bea29a113b111adefb9
Author: Murray Cumming <murrayc murrayc com>
Date:   Thu Apr 21 19:51:27 2016 +0200

    test_accum_iter: Use of decltype(auto).

 tests/test_accum_iter.cc |    3 ++-
 1 files changed, 2 insertions(+), 1 deletions(-)
---
diff --git a/tests/test_accum_iter.cc b/tests/test_accum_iter.cc
index 81ada50..a4fe697 100644
--- a/tests/test_accum_iter.cc
+++ b/tests/test_accum_iter.cc
@@ -25,7 +25,8 @@ struct min_accum
   using result_type = T;
 
   template <typename I>
-  typename std::iterator_traits<I>::value_type operator()(I i1, I i2)
+  decltype(auto)
+  operator()(I i1, I i2)
   {
     return *std::min_element(i1, i2);
   }