[boost] Patch for ifstream_line_iterator_test regression failure

Hello all, I'm attaching a patch for ifstream_line_iterator_test regression failure. It's probably gcc bug (i test it for mingw 3.4.2, but i noticed same error in linux tests), because compiler generates copy constructor for temporary variables and never use it (for those who want to test it in linux environment i'm attaching minimal example). Regards, Janusz