util: fix default termwidth() under Windows
sys.stdout.write('-'*80 + '\n')
or
sys.stdout.write('-'*80 + '\r')
do not work on Windows as they do on unix. On a 80 columns Windows console, the
extra CR or LF are interpreted as if belonging to the next line, so the first
command displays 2 lines (only one on unix) and the second one leave the line
visible and move back to the following line. To avoid this, we sacrifice one
column under Windows.