some concept checking changes as per review comments

[SVN r8268]

concept_checks_fail_expected2.cpp

@@ -0,0 +1,24 @@
+// (C) Copyright Jeremy Siek 2000. Permission to copy, use, modify,
+// sell and distribute this software is granted provided this
+// copyright notice appears in all copies. This software is provided
+// "as is" without express or implied warranty, and with no claim as
+// to its suitability for any purpose.
+
+#include <boost/pending/concept_checks.hpp>
+
+/*
+
+  This file verifies that the BOOST_FUNCTION_REQUIRES2 macro
+  of the Boost Concept Checking Library catches errors
+  when it is suppose to.
+
+*/
+
+struct foo { };
+
+int
+main()
+{
+  BOOST_FUNCTION_REQUIRES2(foo, foo, Comparable2Concept);
+  return 0;
+}