NAME
        SetVBuf -- set buffering modes and size (V39)

   SYNOPSIS
        error = SetVBuf(fh, buff, type, size)
        D0              D1   D2    D3    D4

        long setvbuf(bptr, strptr, long, long)

   FUNCTION
        Changes the buffering modes and buffer size for a filehandle.
        With buff == NULL, the current buffer will be deallocated and a
        new one of (approximately) size will be allocated.  If buffer is
        non-NULL, it will be used for buffering and must be at least
        max(size,208) bytes long, and MUST be longword aligned.  If size
        is -1, then only the buffering mode will be changed.

        Note that a user-supplied buffer will not be freed if it is later
        replaced by another SetVBuf() call, nor will it be freed if the
        filehandle is closed.

        Has no effect on the buffersize of filehandles that were not created
        by allocdosobject().

   INPUTS
        fh   - Filehandle
        buff - buffer pointer for buffered I/O or NULL.  MUST be LONG-aligned!
        type - buffering mode (see <dos/stdio.h>)
        size - size of buffer for buffered I/O (sizes less than 208 bytes
               will be rounded up to 208), or -1.

   RESULT
        error - 0 if successful.  NOTE: opposite of most dos functions!
                NOTE: fails if someone has replaced the buffer without
                using SetVBuf() - runcommand() does this.  remember to
                check error before freeing user-supplied buffers!

   BUGS
        Not implemented until after V39.  From V36 up to V39, always
        returned 0.

   SEE ALSO
        FputC(), fgetc(), ungetc(), flush(), fread(), fwrite(), fgets(),
        fputs(), allocdosobject()