[boost] [iostreams] bug: is_open() should be const

Hi, [referring to latest CVS version] in both class templates boost::iostreams::detail::direct_streambuf and boost::iostreams::detail::indirect_streambuf, member function is_open() is not declared const. However, boost::iostreams::stream<>::is_open() is declared const, so it won't compile as it calls one the former on a data member. Therefore, either all three members are declared const or none of them. The all-const approach makes more sense, IMHO. HTH, Ganesh