arrayOffset() not taken into account by JNI ByteBuffer methods

[blambov]

Changing AbstractLZ4Test.Tester.BYTE_BUFFER to use slicing demonstrates the problem:

    public static final Tester<ByteBuffer> BYTE_BUFFER = new Tester<ByteBuffer>() {

      @Override
      public ByteBuffer allocate(int length) {
        ByteBuffer bb;
        int slice = randomInt(5);
        if (randomBoolean()) {
          bb = ByteBuffer.allocate(length + slice);
        } else {
          bb = ByteBuffer.allocateDirect(length + slice);
        }
        bb.position(slice);
        bb = bb.slice();
        if (randomBoolean()) {
          bb.order(ByteOrder.LITTLE_ENDIAN);
        } else {
          bb.order(ByteOrder.BIG_ENDIAN);
        }
        return bb;
      }

[odaira]

Solved by #65. Thanks!