layerswitcher in IE leaks memory like a seive

dont add circular refs to inputElem. bind them into a context.

note for posterity:

instead of doing:

        this.baseLayersDiv.innerHTML = "";
        this.baseLayerInputs = new Array();
        
        this.dataLayersDiv.innerHTML = "";
        this.dataLayerInputs = new Array();

we should really cycle through and properly destroy each thing. but for now, this works.

as per previous comment, i have refitted this patch so that it does things the proper way, which means cleaning up after itself -- not just letting things slide until the unloadCache() is called. Also, this improvement to the patch fixes a problem in the updateMap() function where we were still relying on the layer to be tagged off of the inputElement (the circular ref we are here deleting)

one little tiny but was leftover from original. this.checked -> this.inputElem.checked

r2918.