Zero-copy zeroCopyReadRanges and releaseBuffer bugs

I found two bugs

1. org.apache.orc.impl.RecordReaderUtils#zeroCopyReadRanges

   ByteBuffer copy = currentBuffer.duplicate();
   copy.position((int) (current.getOffset() - currentOffset)); 

   if currentBuffer position is not 0, copy.position() will set a uncorrect position.
   I think we should use slice() replace duplicate().

1. org.apache.orc.impl.ZeroCopyShims.ZeroCopyAdapter#releaseBuffer
   The parameter `buffer` is not the original buffer from hdfs reading. It is the slice or duplicate of the original buffer.
   This bug is reported at ORC-700.