Check if the modifiers on the event match those on the binding
@private
@param {Object} binding
@param {Ext.EventObject} event
@return {Boolean} True if the event matches the binding
function(binding, e) {
        var keys = ['shift', 'ctrl', 'alt'],
            i = 0,
            len = keys.length,
            val, key;

        for (; i < len; ++i){
            key = keys[i];
            val = binding[key];
            if (!(val === undefined || (val === e[key + 'Key']))) {
                return false;
            }
        }
        return true;
    }