Reduce windows header includes in our own headers. It turns out that absolutely everything that was including windows.h was doing so needlessly; our headers don't need it, so we should just include winsock2.h (since that's where struct timeval is defined). Pre-2.0 code will use the old headers, which include windows.h for them, so we aren't breaking source compatibility with 1.4. This solves the bug where we were leaving WIN32_LEAN_AND_MEAN defined, in roughly the same way that buying an automobile solves the question of what to give your coachman for boxing day.