Computation hSetBuffering hdl mode sets the mode of buffering for handle hdl on subsequent reads and writes.

    * If mode is LineBuffering, line-buffering is enabled if possible.
    * If mode is BlockBuffering size, then block-buffering is enabled if possible. The size of the buffer is n items if size is Just n and is otherwise implementation-dependent.
    * If mode is NoBuffering, then buffering is disabled if possible.

If the buffer mode is changed from BlockBuffering or LineBuffering to NoBuffering, then

    * if hdl is writable, the buffer is flushed as for hFlush;
    * if hdl is not writable, the contents of the buffer is discarded.