Add std::initializer_list to the following containers:

* deque
* map
* multimap
* set
* multiset
* list
* slist

Tested on clant and g++

test/map_test.cpp

@@ -12,6 +12,7 @@
 #include <boost/container/allocator.hpp>
 #include <boost/container/node_allocator.hpp>
 #include <boost/container/adaptive_pool.hpp>
+#include <utility>
 
 #include "print_container.hpp"
 #include "movable_int.hpp"
@@ -345,6 +346,38 @@ int test_map_variants()
    return 0;
 }
 
+template<typename MapType>
+bool test_support_for_initialization_list_for()
+{
+#if !defined(BOOST_NO_CXX11_HDR_INITIALIZER_LIST)
+   const std::initializer_list<std::pair<const int, int>> il
+      = {std::make_pair(1, 2), std::make_pair(3, 4)};
+   const MapType expected(il.begin(), il.end());
+   {
+      const MapType sil = il;
+      if (sil != expected)
+         return false;
+
+      const MapType sil_ordered(ordered_unique_range_t{}, il);
+      if(sil_ordered != expected)
+         return false;
+
+      MapType sil_assign = {std::make_pair(99, 100)};
+      sil_assign = il;
+      if(sil_assign != expected)
+         return false;
+   }
+   {
+      MapType sil;
+      sil.insert(il);
+      if(sil != expected)
+         return false;
+   }
+   return true;
+#endif
+   return true;
+}
+
 int main ()
 {
    //Recursive container instantiation
@@ -421,6 +454,12 @@ int main ()
    if(!boost::container::test::test_propagate_allocator<map_propagate_test_wrapper>())
       return 1;
 
+   if(!test_support_for_initialization_list_for<map<int, int> >())
+      return 1;
+
+   if(!test_support_for_initialization_list_for<multimap<int, int> >())
+      return 1;
+
    ////////////////////////////////////
    //    Test optimize_size option
    ////////////////////////////////////