improve efficiency of fwrite * oct-stream.h, oct-stream.cc (write_int, do_write): Delete. (convert_ints, convert_data, octave_stream::write_bytes octave_stream::skip_bytes): New functions. (octave_stream::write): Improve efficiency by writing data in larger chunks. * oct-stream.cc: Delete unnecessary template instantiations. * data-conv.h, data-conv.cc (is_equivalent_type): New template. Provide specializations for core Octave data types. (oct_data_conv::data_type_size): New function. (oct_data_conv::data_type_to_string): Correct spelling of unsigned.

# u_vr.m

## define and exectute "__demo__" once
eval ("function __demo__ ();  df_vr;  v = vr * 2; endfunction");
__demo__;

## clear definition of "__demo__"
clear __demo__

## define and exectute "__demo__" once more
eval ("function __demo__ ();  df_vr;  v = vr * 2; endfunction");
__demo__;