small fixes so that lib can be compiled in Win32 with Visual Studio 2013 (Express)

1. There is no "main.cpp" in the OSDependent/ directory.
2. VS 2013 does not pull in std::min and std::max without including <algorithm> in Intermediate.cpp
3. YY_NO_UNISTD_H seems to not be implemented/respected by the included bison and flex EXEs, and since this directory is already in the includes, add a dummy "unistd.h" so that compiles work.