Fix box-shadow parsing for IE9

In IE window.getComputedStyle().boxShadow value has different order of color, dimensions and inset parts than in chrome/firefox. Also dimensions count can be less than 4 (as was specified in in the source css). So regexp is changed a little and shadow string is splat by a comma. Every splat part is matched against regexp to extract dimensions. Inset is checked by just using indexOf() on every splat part.