Incomplete work for using Boost.Polygon to compute medial axis

xs/src/boost/is_placeholder.hpp

@@ -0,0 +1,31 @@
+#ifndef BOOST_IS_PLACEHOLDER_HPP_INCLUDED
+#define BOOST_IS_PLACEHOLDER_HPP_INCLUDED
+
+// MS compatible compilers support #pragma once
+
+#if defined( _MSC_VER ) && ( _MSC_VER >= 1020 )
+# pragma once
+#endif
+
+
+//  is_placeholder.hpp - TR1 is_placeholder metafunction
+//
+//  Copyright (c) 2006 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
+
+
+namespace boost
+{
+
+template< class T > struct is_placeholder
+{
+    enum _vt { value = 0 };
+};
+
+} // namespace boost
+
+#endif // #ifndef BOOST_IS_PLACEHOLDER_HPP_INCLUDED