fixed windows file errors and java check

When uploading the tutorial file in formhub, I was getting a permission denied to my temp directory.  This was because pyxform was creating and opening a tempfile, then trying to open it again.  This works fine in Linux, but not so great in Windows (https://docs.python.org/2/library/tempfile.html#tempfile.NamedTemporaryFile).  I also noticed a "which" command, which always returns true in Windows based on the logic.  Checking for the os name and using "where", then checking for the INFO error will work better.