Fix to always use the Java version specified in JAVA_HOME

Here's a nice one... Puts whatever in JAVA_HOME first on the PATH and therefore we can continue to use 'java' to get the correct version. Not the prettiest solution out there but having tried a couple of other approaches this is the first one I have actually made work the way we want it to. 

It's been tested on Windows 8.

Special review by @jroper (whom I know is a huge fan of Windows batch scripts).

What's the scoping in the Windows shell, if you set an environment variable, is it local to the shell, or global?