In addition to my last pull request

With my las commit, everything was working fine in windows, but when I
try under Linux, I realized something :
Under Linux, ghostscript was sending back ink coverages values with
comma as separator (i'm in French LOCALE) , whereas it use point separator under windows.

It also explain the ClassCastException before my last commit -> the
Decimal formatter was expecting comma as separator.

So here is my solution.

Possible limitations -> passing a number formatted as "123,299.33" will rise an exception.