function _mergeOptions(obj1, obj2) {
    var obj3 = {};
    for (var attrname in obj1) { obj3[attrname] = obj1[attrname]; }
    for (var attrname in obj2) { obj3[attrname] = obj2[attrname]; }
    return obj3;
  }
Overwrites obj1's values with obj2's and adds obj2's if non existent in obj1
via: http://stackoverflow.com/questions/171251/how-can-i-merge-properties-of-two-javascript-objects-dynamically

@param obj1
@param obj2
@returns obj3 a new object based on obj1 and obj2