(fs) newFileSystem should not require an environment when opening a file as a file system

jdk-version: jdk7/pit/b123

when newing a zipfs instance, null env map should be allowed to be passed in as a parameter in
public static FileSystem newFileSystem(FileRef file,
                                       Map<String,?> env,
                                       ClassLoader loader)
                                throws IOException
and the alike.

Currently, at leaset an empty map is needed, which seems doesn't make much sense.