[boost] [iostreams] MAP_FILE not available on some platforms

The iostreams module mapped_file.cpp fails to compile on (at least) Solaris because it makes use of the mmap flag MAP_FILE which does not exist on that platform. I think this should be protected in an #ifdef MAP_FILE block or similar. http://tinyurl.com/4gv9p -- Caleb Epstein caleb dot epstein at gmail dot com