Updated Concept Check library documentation.

Changed BOOST_CONCEPT_WHERE to BOOST_CONCEPT_REQUIRES to be more
consistent with the current C++0x proposal, which now uses a
"requires" keyword in lieu of "where."

Factored GCC workarounds into the BOOST_CONCEPT_USAGE macro.


[SVN r40769]

bad_error_eg.cpp

@@ -1,13 +1,14 @@
+#include <vector>
+#include <complex>
+#include "algorithm"
+
+int main()
+{
+    std::vector<std::complex<float> > v;
+    std_::stable_sort(v.begin(), v.end());
+}
+
 // (C) Copyright Jeremy Siek 2000.
 // 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)
-
-#include <list>
-#include <algorithm>
-
-int main() {
-  std::list<int> v;
-  std::stable_sort(v.begin(), v.end());
-  return 0;
-}