--posix option for awk call to avoid problems with locale settings

I had the problem that awk saved ```0.9*l[i]``` with a comma instead of a floating point. As a consequence the python script failed with the error message 
> ValueError: invalid literal for float(): 18,9

By adding the posix option to the awk call we get sure that the right floating point is used despite of your locale configuration.

http://www.gnu.org/software/gawk/manual/html_node/Conversion.html