fix locale problem (decimal separator isn't dot but comma)

If user changes locale with os.setlocale to a "dirty"
locale (which use comma as decimal separator (not dot), e.g.
hu_HU) `tonumber` will produce "0,6" instead of "0.6"
which causes bad comparision.

Signed-off-by: uzsolt <udvzsolt@gmail.com>
Signed-off-by: Uli Schlachter <psychon@znc.in>