This patch enables libboost_iostreams and bumps the magic number to match.

Background:
Ever since I started building blender on linux, I've been plagued by an unknown instability when I try to render various complex scenes. I don't usually have heavy scenes, so this never truly bothered me. With convergence to 2.77, I started to get severe problems. I decided to build entirely against install_deps libraries (I had been building against local LLVM and Boost because they were default in cmake-gui (ignorant me)). This weekend I made a solid, automated build script built against install_deps and in doing so I found that iostreams was the cause of my instability and build error against install_deps Boost (error related to linking libboost_system and libboost_iostreams). It seems iostreams is required by blender.