MPL is broken with GCC 4.5.

https://bugs.gentoo.org/317969
https://svn.boost.org/trac/boost/ticket/4061
https://svn.boost.org/trac/boost/changeset/61467

--- a/boost/mpl/aux_/preprocessed/gcc/template_arity.hpp
+++ b/boost/mpl/aux_/preprocessed/gcc/template_arity.hpp
@@ -83,7 +81,7 @@ template< typename F, int N >
 struct template_arity_impl
 {
     BOOST_STATIC_CONSTANT(int, value =
-          sizeof(arity_helper(type_wrapper<F>(), arity_tag<N>())) - 1
+          sizeof(::boost::mpl::aux::arity_helper(type_wrapper<F>(), arity_tag<N>())) - 1
         );
 };
 
--- a/boost/mpl/aux_/template_arity.hpp
+++ b/boost/mpl/aux_/template_arity.hpp
@@ -98,7 +98,7 @@ template< typename F, BOOST_MPL_AUX_NTTP_DECL(int, N) >
 struct template_arity_impl
 {
     BOOST_STATIC_CONSTANT(int, value = 
-          sizeof(arity_helper(type_wrapper<F>(),arity_tag<N>())) - 1
+          sizeof(::boost::mpl::aux::arity_helper(type_wrapper<F>(),arity_tag<N>())) - 1
         );
 };