Fix slider steps

As reported in #1073 modulus operator `%` can return unexpected results.
This PR adresses and corrects a bug that  didn't allowed to have more
steps than range.

Before (`range [0, 5], steps 10` - decimal steps are ignored):
http://jsfiddle.net/2vTqr/2/
Corrected (decimal steps are not ignored):  http://jsfiddle.net/2vTqr/

fixes #1073