Add is_nothrow_swappable

doc/is_nothrow_swappable.qbk

@@ -0,0 +1,23 @@
+[/ 
+  Copyright 2017 Peter Dimov
+
+  Distributed under the Boost Software License, Version 1.0.
+
+  (See accompanying file LICENSE_1_0.txt or copy at
+  http://www.boost.org/LICENSE_1_0.txt).
+]
+
+[section:is_nothrow_swappable is_nothrow_swappable]
+
+   template <class T>
+   struct is_nothrow_swappable : public __tof {};
+
+__inherit If the expression `swap(declval<T&>(), declval<T&>())` (in a context
+where `std::swap` is visible) is valid and non-throwing, inherits from
+__true_type, otherwise from __false_type.
+
+__compat This trait requires C++11.
+
+__header ` #include <boost/type_traits/is_nothrow_swappable.hpp>` or ` #include <boost/type_traits.hpp>`
+
+[endsect]

doc/type_traits.qbk

@@ -100,6 +100,7 @@
 [def __is_nothrow_move_constructible [link boost_typetraits.reference.is_nothrow_move_constructible is_nothrow_move_constructible]]
 [def __has_nothrow_assign [link boost_typetraits.reference.has_nothrow_assign has_nothrow_assign]]
 [def __is_nothrow_move_assignable [link boost_typetraits.reference.is_nothrow_move_assignable is_nothrow_move_assignable]]
+[def __is_nothrow_swappable [link boost_typetraits.reference.is_nothrow_swappable is_nothrow_swappable]]
 
 [def __is_base_of [link boost_typetraits.reference.is_base_of is_base_of]]
 [def __is_virtual_base_of [link boost_typetraits.reference.is_virtual_base_of is_virtual_base_of]]
@@ -300,6 +301,7 @@ See __has_trivial_constructor.
 [include is_member_pointer.qbk]
 [include is_nothrow_move_assignable.qbk]
 [include is_nothrow_move_constructible.qbk]
+[include is_nothrow_swappable.qbk]
 [include is_object.qbk]
 [include is_pod.qbk]
 [include is_pointer.qbk]