Includes Proto callable ``boost::proto::functional::push_back``.

A PolymorphicFunctionObject type that invokes the `fusion::push_back()` algorithm on its arguments.

A PolymorphicFunctionObject type that invokes the `fusion::push_back()` algorithm on its arguments.

`proto::callable`
This(Seq, T)
fusion::result_of::push_back< typename boost::add_const<typename boost::remove_reference<Seq>::type>::type , typename boost::remove_const<typename boost::remove_reference<T>::type>::type >
typename fusion::result_of::push_back< Seq const, T >::type `Seq const &` `T const &`

`fusion::push_back(seq, t)`