Removed dependency on JNA_LIB and contrib paths.

You can import `jnalib` into a fresh Eclipse project and it will fail in a couple of ways. The first one is that it wants a value for `JNA_LIB`, I am not sure why. The other is that `contrib/platform/src` will be built, which doesn't seem to  work, you should be importing the `contrib/platform` project separately. I think even if it did there're many more `contrib` projects and maybe we should move `platform` one level up, instead of trying to lump it into `jnalib`.