X3: Refactor detectors from disable_if_substitution_failure to just a cast to void

I had to do that to workaround some bug in vs2015 in one detector and have decided to refactor others too.

include/boost/spirit/home/x3/core/parser.hpp

@@ -17,7 +17,6 @@
 #include <boost/spirit/home/x3/support/unused.hpp>
 #include <boost/spirit/home/x3/support/context.hpp>
 #include <boost/spirit/home/x3/support/traits/has_attribute.hpp>
-#include <boost/spirit/home/x3/support/utility/sfinae.hpp>
 #include <boost/core/ignore_unused.hpp>
 #include <boost/assert.hpp>
 #include <string>

include/boost/spirit/home/x3/nonterminal/detail/rule.hpp

@@ -12,7 +12,6 @@
 #include <boost/spirit/home/x3/core/parser.hpp>
 #include <boost/spirit/home/x3/core/skip_over.hpp>
 #include <boost/spirit/home/x3/directive/expect.hpp>
-#include <boost/spirit/home/x3/support/utility/sfinae.hpp>
 #include <boost/spirit/home/x3/nonterminal/detail/transform_attribute.hpp>
 #include <boost/utility/addressof.hpp>
 
@@ -98,15 +97,14 @@ namespace boost { namespace spirit { namespace x3 { namespace detail
 
     template <typename ID, typename Iterator, typename Context>
     struct has_on_error<ID, Iterator, Context,
-        typename disable_if_substitution_failure<
-            decltype(
+            decltype(void(
                 std::declval<ID>().on_error(
                     std::declval<Iterator&>()
                   , std::declval<Iterator>()
                   , std::declval<expectation_failure<Iterator>>()
                   , std::declval<Context>()
                 )
-            )>::type
+            ))
         >
       : mpl::true_
     {};
@@ -116,15 +114,14 @@ namespace boost { namespace spirit { namespace x3 { namespace detail
 
     template <typename ID, typename Iterator, typename Attribute, typename Context>
     struct has_on_success<ID, Iterator, Context, Attribute,
-        typename disable_if_substitution_failure<
-            decltype(
+            decltype(void(
                 std::declval<ID>().on_success(
                     std::declval<Iterator&>()
                   , std::declval<Iterator>()
                   , std::declval<Attribute&>()
                   , std::declval<Context>()
                 )
-            )>::type
+            ))
         >
       : mpl::true_
     {};

include/boost/spirit/home/x3/support/utility/is_callable.hpp

@@ -8,7 +8,6 @@
 #define BOOST_SPIRIT_X3_IS_CALLABLE_HPP_INCLUDED
 
 #include <boost/mpl/bool.hpp>
-#include <boost/spirit/home/x3/support/utility/sfinae.hpp>
 
 namespace boost { namespace spirit { namespace x3 { namespace detail
 {
@@ -16,8 +15,8 @@ namespace boost { namespace spirit { namespace x3 { namespace detail
     struct is_callable_impl : mpl::false_ {};
 
     template <typename F, typename... A>
-    struct is_callable_impl<F(A...), typename disable_if_substitution_failure<
-        decltype(std::declval<F>()(std::declval<A>()...))>::type>
+    struct is_callable_impl<F(A...),
+        decltype(void(std::declval<F>()(std::declval<A>()...)))>
       : mpl::true_
     {};
 }}}}