const qualified return value in iterator_facade

[brian.tyler@…]

This is a very minor thing:

The line:

boost::indirect_iterator<const int* const *> it;

creating a iterator for constant iteration through a container of constant pointers creates a warning

"boost/iterator/iterator_facade.hpp:653: warning: type qualifiers ignored on function return type"

obviously this is not the way to fix it, but changing this line to typename remove_const<typename boost::detail::operator_brackets_result<Derived,Value,reference>::type>::type solves the problem.