_semantic-grid.scss: changed columns on small screen to float:none; width:auto; (non mobile grid)

Using {float:none; width:auto;} on non-mobile-grid columns at small screen. Changed from {float:left; width:100%;}

Reasoning: If Foundation user's aren't employing a mobile grid, columns should always stack on top of each other at small screen; they don't need to float. Changing width from 100% to auto allows additional left/right margin on the element without exceeding parent container's width.

It appears standard Foundation CSS does not have the problem (stylesheets/foundation.css uses {float:none; width:auto;} for non-mobile-grid columns at small screen). 

Minimal test case: http://toddwelstein.com/zurb/small-screen-widths/ 
More about width auto vs. 100%: http://www.456bereastreet.com/lab/width-auto/