/* Deselects the "All" filter if
 * another filter has been selected 
 * and deselects all other filters if all
 * selected. If nothing selected defaults all.
 * 
 */
function validateSelection(option) {
	
	if (option != null) {
		
		var frm = option.form;
		var allSelected = frm.allCat.checked;
		
		if (option.value != "all" && allSelected) {
			frm.allCat.checked = false;
		} else if (option.value == "all") {
			
			for (var i=0; i<parseInt(frm.nrcats.value); i++) {
				eval("document.filtercatsfrm.filterCat_" + i).checked = false;
			}
			option.checked = true;
			
		} else { 
			
			var found = false;
			
			// if none selected default all
			for (var i=0; i<parseInt(frm.nrcats.value); i++) {
				
				if (eval("document.filtercatsfrm.filterCat_" + i).checked) 
					found = true;
					
				if(found) break;
			}
			
			// none checked so select all
			if (!found) {
				frm.allCat.checked = true;
			}	
		}
		
	}	
}