Ant Buildfile, Specific OS should be replaced with OS Family

 Replaced "Windows 7"/"Windows 8" with "windows" osfamily for Windows versions other than 7/8 and replace "Linux"/"Mac OS X" with "unix" osfamily for Unix OSes that aren't Linux/Mac in Ant Buildfile (build.xml).

This means that Windows versions that aren't 7 or 8 can use the buildfile, aswell as other Unix OSes (Linux & Mac OS X are classed as Unix).

It also makes the build file a bit smaller, but whatever.