Fix https://github.com/joeferner/node-java/issues/143

Fixes https://github.com/joeferner/node-java/issues/143 - the threading bug on Windows.  I think it's because the previous code wasn't strictly following the rules on JNI - you can't pass objects (ie the args), nor the JNIEnv across the thread boundary from a Java thread to the V8 main thread.

Also fixes the gyp problems from https://github.com/joeferner/node-java/pull/150, for Windows at least.