Tweaked DOM util opacity to only apply in IE when opacity !== 1

[DamonOehlman]

Had a few issues working with IE and transparent markers. Essentially, the transparent areas of the markers were being displayed with a black background and disabling the filter style fixed the problem.

Not an ideal fix, I know, but tried a few different things (accessing the msFilter property as per http://www.quirksmode.org/css/opacity.html) but had no luck.

[mourner]

Looks reasonable, thanks!

[ajbeaven]

The standard fix for this would be something like this:

.leaflet-marker-icon {
    background: transparent;
    -ms-filter: "progid:DXImageTransform.Microsoft.gradient(startColorstr=#00FFFFFF,endColorstr=#00FFFFFF)"; /* IE8 */   
    filter: progid:DXImageTransform.Microsoft.gradient(startColorstr=#00FFFFFF,endColorstr=#00FFFFFF);   /* IE6 & 7 */      
    zoom: 1;
}