omit unnecessary bits when explicit operator conversions are supported

test/compile-fail/operator_less_2.cpp

@@ -0,0 +1,15 @@
+// Copyright 2018 James E. King III. Use, modification and
+// distribution is subject to 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)
+
+#include <boost/logic/tribool.hpp>
+
+int main(int, char*[])
+{
+  using boost::logic::tribool;
+
+  tribool t(true);
+
+  return t < 1; // expect to see: error: invalid operands to binary expression ('boost::logic::tribool' and 'int')
+}