Bugfixes

- attempt to clean direct memory reserved by a java.nio.DirectByteBuffer.
- ret var. in glfs_java_volume_free function was uninitialized, so randomly could return -1
- swig generates glfs_java_file_length as a int function, so it does not work for files >= 2GB
- use glusterfsio.glfs_java wrapper for java classes, instead of directly glusterfsio.glfs_javaJNI which is internal non-public class.