[boost] [1.34.0] [iostreams] patch for building by BBv2

Hello, I'm testing Boost.Iostreams library for 1.34. Then I found that the libraries built by BBv2 don't contain some classes. This problem occurs because the sources of the "lib boost_iostreams" don't contain the following files except zlib.cpp and bzip2.cpp: file_descriptor.cpp mapped_file.cpp These files were contained in the sources for 1.33.1 (BBv1). So I think that it's a simple mistake. The attachment is the patch for this problem. Regards, Takeshi Mouri