Moved the specialization into namespace boost

[SVN r34477]

test/bind_placeholder_test.cpp

@@ -43,11 +43,16 @@ template< int I > struct custom_placeholder
 {
 };
 
-template< int I > struct boost::is_placeholder< custom_placeholder< I > >
+namespace boost
+{
+
+template< int I > struct is_placeholder< custom_placeholder< I > >
 {
     enum { value = I };
 };
 
+} // namespace boost
+
 int main()
 {
     int const x1 = 1;