Incorrect padding in polyfill browsers without `border-box` box sizing

[karlhorky]

Unless you use box-sizing: border-box, still getting wrong padding with version 1.4.5 on IE11 latest / Win 7.

Testcase IE11: http://jsfiddle.net/41weta35/9/

This does however work properly on the demo website.

Originally reported in #44 (comment)

[karlhorky]

Workaround is to use box-sizing: border-box:

https://jsfiddle.net/41weta35/10/

cc @TKES