Remove buffering to fileio instead of calling fflush

Remove buffering to fileio instead of calling fflush
By default text files are line buffered, and this means that -f option will
not write the line until a \n is printed. This is not very useful for
debugging, so a call to fflush was added. This patch substitute this call
(which will be done by each character painted) by the full remove of the
buffering in the file.
---
 st.c |   12 +++++-------
 1 file changed, 5 insertions(+), 7 deletions(-)