Windows.h instead of windows.h fails to compile when cross compiling on a case sensitive filesystem (MinGW on Linux)
setpgrp(void) doesn't exist on FreeBSD, setpgid(0, 0) is the portable alternative
Merge pull request #19 from troyheron/master

Minor portability fixes.
According to Linux man pages: "The System V-style setpgrp(), which takes no arguments, is equivalent to setpgid(0, 0)."