Biggest integral types for value-based template arguments

[Daryle Walker]

This is based on the post at <​http://lists.boost.org/Archives/boost/2008/07/139965.php>:

The boost::intmax_t and boost::uintmax_t types in "[source:trunk/boost/boost/cstdint.hpp@32397 boost/cstdint.hpp]" alias the largest built-in signed and unsigned integer types. They should be the special 64-bit types, (unsigned) long long or __int64, on systems that support 64-bit registers (and no higher). However, the BOOST_NO_INTEGRAL_INT64_T preprocessor flag warns when these types are not suitable as integral constant expressions. Therefore, there needs to be types that indicate the largest integral types still suitable in integral constant expressions.